Step 3 · 6–8%

Immune, Blood & Multisystem

Anemia, clotting, blood cancers, HIV, allergy, sepsis, poisoning and the environment.

Bleeding, clotting & anticoagulation

Read the platelet count and the clotting times first, then choose the anticoagulant, how long to give it and how to reverse it for the patient in front of you.

Rules to know

Proximal DVT or PE, stable, no cancer or pregnancy → apixaban or rivaroxaban from day one; dabigatran or edoxaban only after 5 days of parenteral heparin
VTE after surgery or another transient major provoker → anticoagulate for 3 months, then stop
Unprovoked VTE or a lasting risk factor → treat 3–6 months, then usually continue indefinitely if bleeding risk is low; reduced-dose apixaban or rivaroxaban suits the extended phase
VTE with active cancer → apixaban, edoxaban, rivaroxaban or LMWH for as long as the cancer is active; favor apixaban or LMWH with luminal GI or GU tumors
Mechanical heart valve or high-risk antiphospholipid syndrome needing anticoagulation → warfarin, not a DOAC; DOACs caused more thrombotic events in these groups
Starting warfarin for VTE → overlap heparin or LMWH for at least 5 days and until the INR is ≥2 for 24 hours
Isolated calf DVT, mild symptoms, low risk of extension → repeat compression ultrasound over 2 weeks; anticoagulate only if it grows toward the popliteal vein
Superficial vein clot ≥5 cm long → fondaparinux 2.5 mg daily for 45 days; within 3 cm of the saphenofemoral junction, treat as a DVT
Proximal DVT or PE but anticoagulation impossible (active bleeding) → retrievable IVC filter; anticoagulate and pull the filter once the bleeding risk passes
Life-threatening bleed on apixaban or rivaroxaban → stop the drug, give andexanet alfa or 4-factor PCC; charcoal if the last dose was about 2 hours ago
Life-threatening bleed on dabigatran → idarucizumab 5 g IV; hemodialysis clears dabigatran if idarucizumab is not available
Major bleed on warfarin → hold warfarin, give 4-factor PCC plus vitamin K 10 mg by slow IV; plasma only when PCC is unavailable
Warfarin with INR 4.5–10 and no bleeding → hold one or two doses and recheck; routine vitamin K adds nothing
Warfarin with INR above 10 and no bleeding → hold warfarin, give oral vitamin K 2.5–5 mg, recheck INR within a day
Bleeding on unfractionated heparin → protamine 1 mg per 100 units given over the past 2–3 hours; protamine only partly reverses LMWH
Platelets halve 5–10 days into heparin, or a new clot → HIT likely; score with the 4T tool and send a PF4 antibody assay
Intermediate or high suspicion of HIT → stop every heparin source including flushes; start argatroban, bivalirudin, fondaparinux or a DOAC before results return
HIT and warfarin planned → start it only after platelets recover to ≥150,000, overlapping the non-heparin agent for at least 5 days
Low platelets alone in a well adult, smear otherwise normal → ITP; test for HIV and hepatitis C; observe if the count is ≥30,000 without bleeding
ITP with platelets under 30,000 or bleeding → prednisone or a short dexamethasone pulse; add IVIG when a fast rise is needed (bleeding, urgent surgery)
ITP relapsing after steroids → thrombopoietin receptor agonist or rituximab; splenectomy only after about 12 months and after vaccination
Schistocytes, very low platelets, hemolysis, maybe fever, confusion or kidney injury → TTP; urgent plasma exchange, steroids, caplacizumab; draw ADAMTS13 first but never wait for it
Child with bloody diarrhea, then hemolysis, low platelets, kidney failure → STEC-HUS; fluids, dialysis if needed; no antibiotics or antimotility drugs
Sick patient oozing with high PT/PTT, low fibrinogen and platelets → DIC; treat the cause (sepsis, trauma, obstetric catastrophe); replace products only for bleeding or procedures
Mucosal bleeding and heavy periods with a normal platelet count → von Willebrand disease; VWF antigen, activity, factor VIII; desmopressin for type 1 minor bleeds
Joint or muscle bleeds in a boy with an isolated long PTT → hemophilia A or B; factor VIII and IX levels; factor replacement, emicizumab prophylaxis for hemophilia A
Long PTT that a 1:1 mixing study does not correct → inhibitor; lupus anticoagulant if the patient clots, acquired factor VIII inhibitor if new bleeding
Thrombophilia testing after a clot with a clear provoker → not indicated; the result does not change duration
Unprovoked clot, arterial clot in a young adult, or recurrent pregnancy loss → antiphospholipid antibodies; confirm positives on repeat testing 12 weeks later
Bleeding in kidney failure with a normal platelet count → uremic platelet dysfunction; desmopressin, effective dialysis, correct the anemia

Traps that cost points

Sending protein C, protein S and antithrombin levels during the acute clot or on anticoagulation→ Clot and drugs lower these levels and create false positives; test only when the answer would change duration, and only after therapy ends.
Transfusing platelets in TTP or HIT without life-threatening bleeding→ Platelets can fuel new thrombosis; the treatment is plasma exchange for TTP and a non-heparin anticoagulant for HIT.
Starting warfarin alone on the day HIT is suspected→ Warfarin lowers protein C first and can cause venous limb gangrene; use a non-heparin anticoagulant and add warfarin after platelets recover. If already given, reverse with vitamin K.
Choosing a DOAC for triple-positive antiphospholipid syndrome→ Trials showed more arterial events on DOACs; warfarin with an INR goal of 2–3 is the drug.
Ordering plasma first for a warfarin-associated brain bleed→ 4-factor PCC corrects the INR within minutes using little volume; add IV vitamin K so the correction lasts.
Treating a well adult with ITP and a platelet count of 60,000→ Above 30,000 without bleeding, observation is correct; steroids add harm without benefit.
Placing an IVC filter in a patient who can take anticoagulants→ Filters do not improve survival and raise later DVT risk; reserve them for patients who truly cannot be anticoagulated.
Giving antibiotics to a child with bloody diarrhea and suspected E coli O157→ Antibiotics may increase toxin release and HUS risk; give fluids and follow the CBC and creatinine.

Anemia & hemoglobin disorders

In the Brain

Sort anemia by MCV and reticulocyte count, find the cause before you transfuse, and know the standing care that keeps sickle cell patients out of crisis.

Rules to know

Any new anemia → MCV, reticulocyte count and a smear; low reticulocytes mean underproduction, high reticulocytes mean bleeding or hemolysis
Microcytic anemia with ferritin under 30 ng/mL → iron deficiency; with active inflammation, a ferritin up to about 100 can still hide it
Iron deficiency in a man or a postmenopausal woman → look for a GI source: upper endoscopy and colonoscopy, plus celiac serology
Oral iron → one dose daily or on alternate days for better absorption and less GI upset; reticulocytes should rise within about a week
Oral iron fails or is not tolerated, malabsorption, CKD, ongoing loss → intravenous iron
Microcytosis, normal ferritin, high red cell count → thalassemia trait; hemoglobin electrophoresis (often normal in alpha trait); no empiric iron
Thalassemia or sickle trait carrier planning pregnancy → test the partner and offer genetic counseling
Chronic illness with low serum iron, low TIBC, normal or high ferritin → anemia of inflammation; treat the disease; iron only if deficiency coexists
Microcytic anemia with ringed sideroblasts on marrow → alcohol, lead, isoniazid (give pyridoxine), copper deficiency or myelodysplasia
Macrocytic anemia → B12 and folate levels; borderline B12 → methylmalonic acid, which is high in B12 lack and normal in folate lack
B12 deficiency → IM B12, or oral 1–2 mg daily, which works even in pernicious anemia; check intrinsic factor antibodies
Macrocytosis with normal B12 and folate → alcohol, liver disease, hypothyroidism, drugs (methotrexate, hydroxyurea, zidovudine) or myelodysplasia in older adults
Suspected hemolysis → LDH up, haptoglobin down, indirect bilirubin up, reticulocytes up; next a direct antiglobulin (Coombs) test
DAT positive for IgG with spherocytes → warm autoimmune hemolysis; prednisone first, rituximab for relapse; look for lupus, CLL or a culprit drug
DAT positive for C3 only, symptoms in the cold → cold agglutinin disease; keep warm, rituximab or sutimlimab; steroids work poorly; look for lymphoma or Mycoplasma
Hemolysis after dapsone, primaquine, nitrofurantoin, rasburicase or fava beans → G6PD deficiency; bite cells, Heinz bodies; stop the trigger, measure G6PD weeks later
Negative DAT, spherocytes, splenomegaly, affected relatives → hereditary spherocytosis; EMA binding test; folic acid; splenectomy only for severe disease
Hemolysis plus clots in odd sites (hepatic, portal, cerebral veins) and cytopenias → PNH; flow cytometry; complement inhibitor after meningococcal vaccination
Pancytopenia, empty marrow, no splenomegaly → aplastic anemia; young with a matched donor → transplant; others → ATG, cyclosporine and eltrombopag
Sickle cell pain crisis → IV opioid within an hour of arrival and frequent reassessment; fluids only if dry; incentive spirometry
Sickle cell with chest pain, fever, hypoxia, new infiltrate → acute chest syndrome; oxygen, ceftriaxone plus a macrolide, transfuse; exchange transfusion if worsening
Sickle cell disease with fever ≥38.5 °C → blood culture, CBC and IV ceftriaxone at once; functional asplenia invites pneumococcal sepsis
Sickle cell disease with sudden pallor and very low reticulocytes → parvovirus B19 aplastic crisis; transfuse, droplet precautions
Sickle cell child with falling hemoglobin and a rapidly enlarging spleen → splenic sequestration; fluids and careful small-volume transfusion
Sickle cell disease, standing care → hydroxyurea from 9 months of age to raise fetal hemoglobin and cut crises; follow CBC for cytopenias
Child with HbSS → penicillin prophylaxis until age 5, full pneumococcal and meningococcal vaccines, yearly transcranial Doppler from age 2 to 16
Sickle cell disease with acute stroke → exchange transfusion now, then a lifelong chronic transfusion program
Stable inpatient without active bleeding → transfuse red cells at hemoglobin under 7 g/dL (8 with heart disease or cardiac/orthopedic surgery), one unit at a time
Chronically transfused patient (thalassemia major, sickle cell) → iron chelation once ferritin passes about 1,000; deferasirox, watching kidney and liver function
Priapism lasting over 4 hours in sickle cell disease → urology for aspiration and intracavernous phenylephrine

Traps that cost points

Giving iron for every microcytic anemia→ Check ferritin first; thalassemia trait and anemia of inflammation do not respond, and extra iron can cause overload.
Starting folate alone for a macrocytic anemia→ Folate can correct the blood count while B12 nerve damage keeps progressing; check B12 or methylmalonic acid first.
Measuring G6PD activity in the middle of a hemolytic episode→ The oldest, enzyme-poor cells have already lysed, so the level reads falsely normal; repeat it 2–3 months later.
Transfusing a sickle cell patient to a hemoglobin of 12→ Viscosity rises and can provoke occlusion; keep the post-transfusion hemoglobin near 10 g/dL or use exchange transfusion.
Blaming diet for iron deficiency in an older adult→ Occult GI cancer must be excluded with upper endoscopy and colonoscopy, even if the stool test is negative.
Holding opioids in a sickle pain crisis until labs return→ Treat pain within the hour and reassess often; undertreatment worsens outcomes. Avoid meperidine.
Using steroids as the main treatment for cold agglutinin disease→ Cold antibodies respond poorly to steroids; keep the patient warm, warm infused fluids, and use rituximab or a complement inhibitor.
Transfusing a stable ICU patient to keep hemoglobin above 10→ A restrictive threshold of 7 g/dL is as safe and spares exposure; transfuse above it only for active bleeding or ischemia.

Poisoning, antidotes & environmental emergencies

In the Brain

Stabilize first, check the levels that hide (acetaminophen, salicylate), match the toxidrome to its antidote, and know when heat, cold, altitude or a bite needs more than supportive care.

Rules to know

Any intentional or unknown overdose → airway, bedside glucose, ECG, acetaminophen and salicylate levels, pregnancy test, call poison control
Activated charcoal → within 1–2 hours of a dangerous ingestion with a protected airway; useless for iron, lithium, alcohols, metals or caustics
Single acetaminophen ingestion with a known time → plot a level drawn at 4 hours or later on the nomogram; at or above the line → N-acetylcysteine
Acetaminophen ingestion at an unknown time, repeated excess dosing, or high AST → start N-acetylcysteine now; the nomogram does not apply
Tinnitus, vomiting, fast breathing, respiratory alkalosis with anion-gap acidosis → salicylate; IV bicarbonate to urine pH 7.5–8, keep potassium normal
Salicylate toxicity with confusion, pulmonary edema, kidney failure or very high level → hemodialysis
Pinpoint pupils and slow breathing → opioid; naloxone in small doses titrated to adequate breathing; infusion for long-acting opioids; naloxone kit at discharge
Seizure, QRS over 100 ms, anticholinergic signs after an antidepressant → tricyclic toxicity; IV sodium bicarbonate boluses, benzodiazepines for seizures
Bradycardia, hypotension, hypoglycemia, wheeze after an overdose → beta-blocker; atropine, fluids, glucagon, high-dose insulin with dextrose
Bradycardia and hypotension with high glucose after an overdose → calcium channel blocker; IV calcium, high-dose insulin with dextrose, vasopressors
Nausea, yellow-tinged vision, bidirectional VT, high potassium on digoxin → digoxin toxicity; digoxin-specific Fab for dysrhythmia, potassium above 5 or organ injury
Anion-gap acidosis with an osmolar gap, blurred vision or oxalate crystals → methanol or ethylene glycol; fomepizole, hemodialysis for severe acidosis or organ damage
Headache and nausea in several household members on a cold day → carbon monoxide; co-oximetry (pulse oximetry reads falsely normal), 100% oxygen by nonrebreather
Carbon monoxide with syncope, coma, seizure, pregnancy, ischemia or very high COHb → discuss hyperbaric oxygen
House-fire victim with coma, hypotension and lactate above 8 → cyanide; IV hydroxocobalamin
Chocolate-brown blood, SpO2 stuck near 85% after dapsone or benzocaine → methemoglobinemia; methylene blue unless G6PD deficient
Miosis, drooling, bronchorrhea, bradycardia, twitching after pesticide exposure → organophosphate; strip clothes, wash skin, atropine until secretions dry, pralidoxime
Hot dry skin, wide pupils, urinary retention, delirium → anticholinergic toxicity; benzodiazepines and cooling; physostigmine only in selected cases
Agitation, fast heart, high temperature, chest pain after cocaine or methamphetamine → benzodiazepines first, active cooling; nitroglycerin and aspirin for chest pain
Tremor, ataxia, confusion and vomiting on lithium → toxicity; stop lithium, IV saline; hemodialysis for severe neurologic signs or kidney failure
Iron overdose with vomiting, GI bleeding, acidosis → IV deferoxamine; whole-bowel irrigation if pills show on x-ray
Benzodiazepine overdose → supportive care; avoid flumazenil in chronic users or mixed overdoses because of seizures
Child with blood lead ≥3.5 µg/dL → confirm on a venous sample, find and remove the source; oral succimer at ≥45; admit for IV chelation at ≥70 or encephalopathy
Core temperature ≥40 °C with confusion after heat exposure → heat stroke; rapid cooling (cold-water immersion for exertional cases) to about 39 °C; antipyretics do nothing
Muscle rigidity, rising end-tidal CO2 and fever under anesthesia → malignant hyperthermia; stop the trigger, IV dantrolene, cool; test relatives
Moderate or severe hypothermia → move gently to avoid VF, active rewarming; in arrest → prolonged CPR and extracorporeal rewarming
Frostbite → rapid rewarming in 37–39 °C water; amputation decisions wait weeks until tissue demarcates
Headache and nausea after rapid ascent → acute mountain sickness; stop climbing, descend if worse; acetazolamide prevents it
Dyspnea at altitude → HAPE: descend, oxygen, nifedipine; ataxia or confusion → HACE: descend, dexamethasone
Joint pain, rash or neurologic signs after a scuba ascent → decompression sickness; 100% oxygen and transfer for hyperbaric treatment
Pit viper bite → immobilize at heart level, no tourniquet, ice or incision; antivenom for progressive swelling, coagulopathy or systemic signs
Spider bite with cramps and a rigid abdomen → black widow; analgesia, benzodiazepines; necrotic ulcer → brown recluse, wound care only

Traps that cost points

Waiting for a 4-hour acetaminophen level in a patient who arrives 12 hours after ingestion→ Start N-acetylcysteine immediately while the level and liver tests run; delay beyond 8 hours raises liver injury.
Intubating a salicylate overdose without matching the prior breathing rate→ Losing the respiratory alkalosis lets acid drive salicylate into the brain; set a high minute ventilation and arrange dialysis.
Giving flumazenil to an unresponsive patient with an unknown ingestion→ It can precipitate seizures in benzodiazepine-dependent patients or tricyclic overdose; support the airway instead.
Trusting a normal pulse oximeter reading in suspected carbon monoxide poisoning→ Oximeters read carboxyhemoglobin as oxygenated; order co-oximetry and give 100% oxygen while waiting.
Giving methylene blue to a patient with G6PD deficiency→ It can trigger hemolysis and fails without NADPH; use ascorbic acid, exchange transfusion or hyperbaric oxygen.
Treating heat stroke with acetaminophen→ The hypothalamic set point is normal; only external cooling lowers the temperature.
Pushing a full 2 mg naloxone dose in a breathing, opioid-dependent patient→ Abrupt withdrawal brings vomiting, aspiration and agitation; titrate small doses to breathing, not to full alertness.
Applying a tourniquet or ice to a snakebite→ Both worsen local tissue injury; immobilize the limb, mark swelling progression and give antivenom if indicated.
Giving activated charcoal for a lithium or iron overdose→ Charcoal does not bind them; use whole-bowel irrigation for iron and saline or dialysis for lithium.

Sepsis, fever, tick-borne & travel infections

In the Brain

Treat sepsis on the clock, work up prolonged fever without shotgun antibiotics, think malaria in every febrile traveler and doxycycline for every sick tick bite, and isolate the right way.

Rules to know

Suspected sepsis with hypotension or lactate ≥4 → blood cultures, then antibiotics within 1 hour; 30 mL/kg balanced crystalloid within 3 hours
MAP under 65 despite fluids → norepinephrine first; a peripheral line is acceptable to start; target MAP ≥65
Still hypotensive on moderate-dose norepinephrine → add vasopressin; ongoing vasopressor need → hydrocortisone 200 mg per day
Choosing resuscitation fluid → lactated Ringer or another balanced crystalloid over normal saline; avoid starches
Initial lactate above 2 → repeat within 2–4 hours; guide resuscitation by lactate clearance and capillary refill
Drainable source (abscess, blocked ureter or bile duct, infected line) → source control as soon as practical, ideally within 6–12 hours
Day 2–3 of empiric antibiotics with culture results → narrow to the organism; stop if infection is ruled out
Falling procalcitonin → supports stopping antibiotics in pneumonia or sepsis; never the only reason to withhold them from a sick patient
Fever, sunburn-like rash, hypotension with a tampon or nasal packing → toxic shock; remove the source, vancomycin plus clindamycin; streptococcal → penicillin plus clindamycin
Fever ≥38.3 °C for ≥3 weeks, unexplained after basic tests → FUO; think infection, cancer, inflammatory disease
FUO workup → travel, animal and drug history, CBC, ESR/CRP, blood cultures, HIV, urinalysis, CT chest/abdomen/pelvis; PET-CT next
Expanding erythema migrans after a tick bite in an endemic area → clinical diagnosis; doxycycline for 10 days; no serology
Ixodes tick attached ≥36 hours, removed within 72 hours, high-incidence area → single 200 mg dose of doxycycline
Lyme carditis with PR ≥300 ms or symptoms → admit, IV ceftriaxone, telemetry; temporary pacing if needed
Lyme facial palsy → oral doxycycline 14 days; Lyme arthritis with a large knee effusion → oral doxycycline 28 days
Tick bite, fever, headache, then rash spreading from wrists and ankles → Rocky Mountain spotted fever (rash reaches palms and soles); doxycycline at once, any age
Tick bite, fever, low WBC and platelets, high transaminases, no rash → ehrlichiosis or anaplasmosis; doxycycline
Fever and hemolysis after Northeast tick exposure, especially without a spleen → babesiosis; smear or PCR; atovaquone plus azithromycin; exchange transfusion if severe
Fever within 3 months of travel to a malaria area → malaria until proven otherwise; thick and thin smears every 12–24 hours for 3 sets
Severe falciparum malaria (altered mental status, parasitemia ≥5%, shock, acidosis, kidney failure) → IV artesunate in the ICU
Uncomplicated falciparum malaria → artemether-lumefantrine or atovaquone-proguanil; vivax or ovale → add primaquine or tafenoquine after a G6PD test
Malaria prophylaxis before travel → atovaquone-proguanil, doxycycline or mefloquine by region and patient; chloroquine only where parasites remain sensitive
Fever, eye-socket pain, myalgia, rash, low platelets after tropical travel → dengue; acetaminophen and fluids, no NSAIDs; admit for warning signs
Fever, abdominal pain, relative bradycardia, rose spots after South Asia travel → enteric fever; blood cultures; ceftriaxone or azithromycin given fluoroquinolone resistance
Freshwater exposure, red eyes without discharge, calf pain, jaundice, kidney injury → leptospirosis; doxycycline, or IV penicillin or ceftriaxone if severe
Unpasteurized dairy, relapsing fevers, sweats, back or joint pain → brucellosis; doxycycline plus rifampin for 6 weeks
Fever with bleeding after travel to an outbreak region → isolate first and call public health before any testing (viral hemorrhagic fever)
TB, measles, varicella, disseminated zoster → airborne isolation in a negative-pressure room with N95 respirators; add contact precautions for varicella and zoster
Influenza, pertussis, meningococcus, mumps → droplet precautions with a surgical mask for close contact
C difficile, MRSA, scabies, norovirus → contact precautions with gown and gloves; soap-and-water handwashing for C difficile and norovirus

Traps that cost points

Holding antibiotics in septic shock until the CT shows the source→ Cultures, then antibiotics within the hour; imaging and drainage follow and must not delay the first dose.
Adding hydrocortisone for every patient with sepsis→ Steroids help only patients who need ongoing vasopressors; they do not benefit sepsis without shock.
Avoiding doxycycline in a young child with suspected Rocky Mountain spotted fever→ Short courses do not stain teeth, and delay raises mortality; doxycycline is first line at every age.
Ordering Lyme serology for a classic erythema migrans rash→ Antibodies are often absent in the first weeks; diagnose clinically and treat.
Letting one negative malaria smear rule out malaria→ Parasitemia fluctuates; repeat smears every 12–24 hours until three are negative.
Giving ibuprofen for fever and pain in dengue→ NSAIDs and aspirin raise bleeding risk with low platelets; use acetaminophen and fluids.
Starting empiric antibiotics or steroids in a stable patient with FUO→ They blur cultures and biopsies and delay the diagnosis; treat empirically only if the patient is unstable or neutropenic.
Using alcohol hand gel after caring for a patient with C difficile→ Alcohol does not kill spores; wash with soap and water and keep contact precautions.

HIV, immunodeficiency & the immunocompromised host

In the Brain

Test widely, start ART at diagnosis, give prophylaxis by CD4 count, offer PrEP and PEP, and recognize the infection pattern that names an immune defect.

Rules to know

Ages 15–65 and every pregnancy → screen for HIV at least once; repeat at least yearly with ongoing risk
HIV screening test → 4th-generation antigen/antibody immunoassay; reactive → HIV-1/2 differentiation assay; discordant result → HIV RNA
Fever, rash, sore throat, nodes 2–4 weeks after a risky exposure → acute HIV; HIV RNA plus antigen/antibody test (antibody may still be negative)
New HIV diagnosis → start ART the same day or as soon as possible, at any CD4 count
New HIV baseline labs → CD4, viral load, genotype, HLA-B*5701, hepatitis A, B and C, syphilis, TB test, creatinine, urinalysis, lipids, glucose
First ART regimen → bictegravir/emtricitabine/TAF or dolutegravir plus two NRTIs; dolutegravir/lamivudine if no hepatitis B and viral load under 500,000
HIV with hepatitis B → regimen must contain tenofovir plus emtricitabine or lamivudine; stopping it can trigger a hepatitis flare
Abacavir → only after a negative HLA-B*5701 test; hypersensitivity can be fatal on rechallenge
After starting ART → viral load in 4–8 weeks, undetectable by about 24 weeks, then every 3–6 months
Viral load undetectable for 6 months on ART → no sexual transmission (undetectable equals untransmittable); tell the patient
CD4 under 200 or oral thrush → TMP-SMX for Pneumocystis; dapsone or atovaquone if sulfa allergic
CD4 under 100 with positive Toxoplasma IgG → daily double-strength TMP-SMX covers toxoplasma as well
CD4 under 50 and ART starting now → no MAC prophylaxis needed
Stopping Pneumocystis prophylaxis → CD4 above 200 for at least 3 months on ART
HIV with active TB → TB drugs first; ART within 2 weeks if CD4 under 50, within 8 weeks otherwise; check rifamycin interactions
HIV with cryptococcal meningitis → amphotericin plus flucytosine, repeat LPs for high opening pressure; delay ART 4–6 weeks
Known infection worsens weeks after ART starts as CD4 climbs → IRIS; continue ART, treat the infection, steroids if severe
CD4 under 100 with ring-enhancing brain lesions → treat for toxoplasmosis; biopsy for CNS lymphoma if no response in 2 weeks
PrEP candidate with sexual or injection risk → oral TDF/FTC, oral TAF/FTC (not for receptive vaginal sex), cabotegravir IM every 2 months, or lenacapavir SC twice yearly
Before and during PrEP → HIV test at start and at each visit (add HIV RNA for injectables), kidney function on oral drugs, STI screening
High-risk sexual or needle exposure within 72 hours → PEP as soon as possible: bictegravir/FTC/TAF or dolutegravir plus TDF/FTC for 28 days; baseline HIV test
Asplenia or before elective splenectomy → pneumococcal, MenACWY, MenB and Hib vaccines, at least 2 weeks before surgery; standby antibiotic for fever
Fever in a patient without a spleen → treat as overwhelming sepsis: blood cultures and IV ceftriaxone (plus vancomycin) without delay
Adult with recurrent sinopulmonary infections, low IgG and IgA, poor vaccine response → common variable immunodeficiency; immunoglobulin replacement
Anaphylaxis to blood products, frequent sinopulmonary infections, Giardia → selective IgA deficiency; washed or IgA-deficient blood products
Recurrent Neisseria infections → terminal complement deficiency; CH50 screen; meningococcal vaccines
Recurrent S aureus, Aspergillus or Serratia abscesses with granulomas → chronic granulomatous disease; dihydrorhodamine test; TMP-SMX and itraconazole prophylaxis
Infant with thrush, chronic diarrhea, poor growth, very low lymphocytes → SCID; no live vaccines, irradiated blood, urgent transplant referral
Boy over 6 months, recurrent bacterial infections, tiny tonsils, no B cells → X-linked agammaglobulinemia; immunoglobulin replacement
Before a TNF inhibitor, rituximab or prolonged high-dose steroids → screen latent TB, hepatitis B and C; live vaccines at least 4 weeks before
Prednisone ≥20 mg daily for ≥4 weeks plus another immunosuppressant → Pneumocystis prophylaxis with TMP-SMX
Transplant recipient 1–6 months out with fever, low white count, hepatitis → CMV; quantitative PCR; ganciclovir or valganciclovir

Traps that cost points

Waiting for the CD4 count or genotype before starting ART→ Start at diagnosis; adjust the regimen when resistance and HLA results return. Early ART improves outcomes and stops transmission.
Starting ART in the first week of cryptococcal meningitis→ Early ART raised mortality from IRIS; begin antifungals now and ART after 4–6 weeks.
Stopping ART when IRIS appears→ IRIS reflects immune recovery; continue ART, treat the infection and add steroids for severe inflammation.
Starting PrEP without excluding acute HIV→ Two-drug PrEP in undiagnosed HIV breeds resistance; test before starting and send HIV RNA if there are recent symptoms.
Giving MMR or varicella vaccine when the CD4 count is under 200→ Live vaccines can cause disseminated disease; give them only when CD4 is 200 or higher.
Choosing dolutegravir/lamivudine for a patient with hepatitis B→ Lamivudine alone breeds HBV resistance; use a tenofovir-containing regimen.
Prescribing TAF/FTC PrEP for a cisgender woman→ It was not studied for receptive vaginal sex; use TDF/FTC or an injectable option.
Advising an asplenic patient with fever to wait and see→ Encapsulated-organism sepsis can kill within hours; take the standby antibiotic and seek care the same day.

Allergy, anaphylaxis & drug reactions

In the Brain

Give IM epinephrine first and fast, tell bradykinin swelling from histamine swelling, and remove penicillin allergy labels that are not real.

Rules to know

Hives or swelling plus breathing, blood pressure or GI symptoms → anaphylaxis; IM epinephrine 0.01 mg/kg (max 0.5 mg) into the thigh now
Anaphylaxis not better 5–15 minutes after the first dose → repeat IM epinephrine; lay the patient flat with legs raised; rapid crystalloid bolus for hypotension
Anaphylaxis refractory to two or three IM doses → IV epinephrine infusion in a monitored setting; early airway for stridor or tongue swelling
Anaphylaxis in a patient on a beta-blocker, poor response to epinephrine → IV glucagon
Antihistamines and steroids in anaphylaxis → comfort adjuncts only; they never replace or delay epinephrine
After anaphylaxis resolves → observe several hours (longer if severe), prescribe two epinephrine devices, give a written action plan, refer to allergy
Unsure whether an episode was anaphylaxis → serum tryptase within about 2 hours of onset, compared with a baseline level later
Lip and tongue swelling without hives on an ACE inhibitor → bradykinin angioedema; secure the airway, stop the drug for life; epinephrine often fails
Recurrent swelling without hives, abdominal pain attacks, affected relatives → hereditary angioedema; low C4 screens, then C1 inhibitor level and function
Hereditary angioedema attack → C1 inhibitor concentrate, icatibant or ecallantide; plasma if none available; short-term prophylaxis before dental or airway procedures
Hives for under 6 weeks → acute urticaria from infection, drug or food; nonsedating antihistamine; no lab workup
Hives on most days for ≥6 weeks → chronic spontaneous urticaria; second-generation antihistamine up to 4 times the usual dose, then omalizumab; minimal labs
Individual hives lasting over 24 hours that burn and leave bruising → urticarial vasculitis; skin biopsy and complement levels
Penicillin label from a remote rash or vague history → low risk; direct oral amoxicillin challenge, then remove the label
Penicillin history of anaphylaxis or recent hives → skin testing, then oral challenge if negative
True penicillin allergy, penicillin essential (syphilis in pregnancy, neurosyphilis) → desensitization in a monitored setting
Non-severe penicillin allergy needing a cephalosporin → give it; past penicillin anaphylaxis → choose one with a dissimilar side chain such as cefazolin
SJS/TEN, DRESS or another severe organ-involving drug reaction → never rechallenge or desensitize; record the drug permanently
Fever, rash, arthralgia, low complement 1–2 weeks after antivenom or drug → serum sickness (monoclonal antibodies too); stop the agent, antihistamine, NSAID; steroids if severe
Suspected food allergy → specific IgE or skin prick to the suspected food only; oral food challenge is the reference test
Itchy mouth from raw fruit, cooked fruit tolerated, pollen allergy → oral allergy syndrome; avoid the raw form; epinephrine rarely needed
Systemic reaction to an insect sting → venom IgE or skin testing, venom immunotherapy, carry epinephrine
Swelling over 10 cm around a sting without systemic signs → large local reaction; cold, antihistamine, short steroid course; no venom testing
Prior moderate or severe contrast reaction → use a different agent and premedicate with steroid plus antihistamine; seafood allergy is irrelevant
Upper-body flushing and itch during a fast vancomycin infusion → infusion reaction; slow the rate, give an antihistamine; not an allergy
Asthma, nasal polyps, reactions to aspirin and other NSAIDs → aspirin-exacerbated respiratory disease; avoid NSAIDs or desensitize; leukotriene blocker
Egg allergy of any severity → any age-appropriate influenza vaccine with routine precautions
Anaphylaxis after a previous dose of a vaccine or its component → contraindication to that vaccine; allergy evaluation
Recurrent flushing and anaphylaxis with baseline tryptase above 20 → systemic mastocytosis; marrow biopsy and KIT mutation testing

Traps that cost points

Giving diphenhydramine first for hives with wheeze and low blood pressure→ That is anaphylaxis; IM epinephrine comes first, and antihistamines only ease the skin symptoms.
Pushing undiluted 1 mg/mL epinephrine IV in a patient who has a pulse→ IV boluses cause arrhythmia and stroke; use the 1 mg/mL product IM, and reserve IV epinephrine for a dilute titrated infusion.
Injecting epinephrine subcutaneously into the arm→ Absorption is slower; inject IM into the anterolateral thigh.
Avoiding every cephalosporin in a patient with a penicillin label→ Cross-reactivity is low and depends on side chains; give the needed cephalosporin, choosing a dissimilar side chain after anaphylaxis.
Switching ACE inhibitor angioedema to a different ACE inhibitor→ It is a class effect; use another drug class. An ARB carries a small risk and needs counseling.
Sending a patient home after anaphylaxis without an epinephrine device→ Symptoms can return hours later or with the next exposure; prescribe two devices and teach their use.
Ordering a broad allergy panel for a first episode of hives→ Acute urticaria is usually from infection or a recent exposure; panels are low yield and produce false positives.
Canceling a contrast study because of a shellfish allergy→ Seafood allergy does not predict contrast reactions; only a prior contrast reaction matters.
Ordering skin tests before challenging a low-risk penicillin history→ A direct oral amoxicillin challenge is safe and faster for low-risk histories.

Transfusion reactions & oncologic emergencies

In the Brain

Stop the transfusion and name the reaction by its timing and signs; in cancer patients, act fast on fever with neutropenia, high calcium, tumor lysis, SVC obstruction and cord compression.

Rules to know

Fever, flank pain, hypotension, dark urine minutes into a transfusion → acute hemolytic reaction (ABO mismatch); stop, fluids, recheck identity, DAT, call the blood bank
Fever and chills during a transfusion, stable, no hemolysis → febrile nonhemolytic reaction; stop, exclude hemolysis and contamination, acetaminophen; leukoreduction prevents it
Hives only during a transfusion → pause, give an antihistamine, resume slowly once symptoms clear
Wheeze, hypotension, angioedema seconds into a transfusion in an IgA-deficient patient → anaphylaxis; stop, IM epinephrine; future washed or IgA-deficient products
Hypoxemia, bilateral infiltrates within 6 hours of transfusion, no volume overload → TRALI, often with hypotension; stop, oxygen or ventilation; no diuretics
Dyspnea, hypertension, raised neck veins during transfusion in heart failure → TACO (older adults and kidney failure too); stop, diuretic, slower rates next time
Hemoglobin drop, jaundice, new positive DAT 3–14 days after transfusion → delayed hemolytic reaction; supportive care, record the antibody
High fever and shock during a platelet transfusion → bacterial contamination; stop, culture the bag and the patient, broad antibiotics
Massive hemorrhage needing many units → plasma, platelets and red cells near 1:1:1; replace calcium, keep warm; tranexamic acid within 3 hours of trauma
Stem cell transplant, Hodgkin lymphoma or purine-analog therapy → irradiated blood products to prevent transfusion-associated GVHD
Fever with ANC under 500 → neutropenic fever (one reading ≥38.3 °C or ≥38.0 °C for an hour); cultures and an antipseudomonal beta-lactam within 60 minutes
Neutropenic fever regimen → cefepime, piperacillin-tazobactam or meropenem; add vancomycin only for line or skin infection, pneumonia, MRSA history or instability
Low-risk neutropenic fever (MASCC ≥21), reliable, near care → oral ciprofloxacin plus amoxicillin-clavulanate at home after the first dose
Neutropenic fever still present after 4–7 days of antibiotics → CT chest and an empiric antifungal such as an echinocandin or voriconazole
Chemotherapy with ≥20% risk of febrile neutropenia → primary prophylaxis with G-CSF
Bulky lymphoma or leukemia about to start chemotherapy → IV fluids plus allopurinol; rasburicase for the highest risk after a G6PD check
After chemotherapy: high potassium, phosphate and uric acid, low calcium, rising creatinine → tumor lysis syndrome; fluids, rasburicase, treat hyperkalemia, dialysis if refractory
Cancer with confusion, polyuria and calcium above 14 → IV saline first, then zoledronic acid; calcitonin covers the first 48 hours; denosumab if kidneys fail
Hypercalcemia in cancer with a suppressed PTH → PTHrP for squamous, kidney or breast tumors; high 1,25-vitamin D in lymphoma responds to steroids
Face and arm swelling, distended chest veins, lung cancer or lymphoma → SVC syndrome; CT chest and a tissue diagnosis first; stent for severe symptoms
SVC syndrome with stridor or cerebral edema → emergency endovascular stenting before the diagnosis is made
Cancer patient with new back pain and a normal exam → MRI of the whole spine within about 24 hours
Cancer with back pain plus weakness, a sensory level or retention → dexamethasone now, emergency whole-spine MRI, then radiation or surgery
Cord compression at one level, good prognosis, unstable spine or radioresistant tumor → surgical decompression, then radiation
Diarrhea, cough, rash, hepatitis or fatigue on a checkpoint inhibitor → immune-related adverse event; hold the drug, steroids by grade; check TSH, cortisol, glucose

Traps that cost points

Giving furosemide first for severe hypercalcemia→ These patients are volume depleted; restore volume with saline, and use a loop diuretic only for fluid overload.
Giving rasburicase without checking G6PD→ It causes hemolysis and methemoglobinemia in G6PD deficiency; use allopurinol and fluids instead.
Waiting for the MRI before giving dexamethasone to a cancer patient with leg weakness→ Steroids given early preserve function; dose them on suspicion and image right after.
Radiating SVC syndrome before a biopsy in a stable patient→ Radiation can ruin the histology, and most cases are not emergencies; get tissue first unless the airway or brain is threatened.
Treating TRALI with diuretics→ TRALI is a capillary leak, not overload, and patients are often hypotensive; give oxygen and ventilatory support.
Taking a rectal temperature or doing a rectal exam in a neutropenic patient→ Mucosal trauma can seed bacteremia; use oral or other routes.
Correcting asymptomatic low calcium in tumor lysis syndrome→ Added calcium binds high phosphate and deposits in tissues and kidneys; give calcium only for tetany, seizures or arrhythmia.
Waiting for a source before treating fever in a neutropenic patient→ Most never show a source; cultures, then antibiotics within an hour, because untreated bacteremia progresses quickly.

Lymph nodes, leukemia, lymphoma & myeloma

In the Brain

Decide which node needs a biopsy and which can wait, recognize each blood cancer from its smear and labs, and know the few that need treatment within hours.

Rules to know

Small tender node after a recent infection, no red flags → observe 3–4 weeks; biopsy if it persists or grows
Node over 2 cm, hard, fixed, supraclavicular, or with B symptoms → excisional or core biopsy; a fine-needle sample cannot classify lymphoma
Left supraclavicular node → look below the diaphragm (stomach, pancreas, pelvis); right supraclavicular → lung, mediastinum, esophagus
Young adult with fever, sore throat, posterior neck nodes, atypical lymphocytes → mononucleosis; heterophile test; no contact sports for at least 3–4 weeks
Mono-like illness with a negative heterophile test → CMV, toxoplasmosis and acute HIV (HIV RNA plus antigen/antibody test)
Tender node draining a kitten scratch → Bartonella; supportive care; azithromycin for bulky nodes or an immunocompromised host
Painless rubbery neck node, night sweats, Reed-Sternberg cells → Hodgkin lymphoma; PET-CT staging; high cure rate with chemotherapy
Chest radiation for Hodgkin lymphoma before age 30 → yearly mammogram plus breast MRI from age 25 or 8 years after radiation, whichever comes later
Older adult with lymphocytes over 5,000 and smudge cells → CLL; flow cytometry; observe until symptoms, cytopenias or bulky disease
Huge white count with basophils and every stage of maturation, big spleen → CML; BCR-ABL by PCR or FISH; tyrosine kinase inhibitor
Blasts on the smear with fatigue, bleeding and infections → acute leukemia; admit, marrow biopsy, check DIC and tumor lysis labs
Suspected acute promyelocytic leukemia (Auer rods, DIC) → start all-trans retinoic acid immediately, before genetic confirmation
White count over 100,000 with hypoxia or confusion → leukostasis; hydroxyurea and leukapheresis; hold red cell transfusion
Young child with pallor, bruising, bone pain, big liver and spleen → acute lymphoblastic leukemia; smear and marrow; best prognosis between ages 1 and 10
Fast-growing jaw or abdominal mass, starry-sky pattern, very high LDH → Burkitt lymphoma; tumor lysis prevention before chemotherapy
Bone pain, anemia, high calcium, kidney injury, high total protein → myeloma; SPEP with immunofixation, serum free light chains, whole-body low-dose CT
Small M-spike, marrow plasma cells under 10%, no organ damage → MGUS (M-protein under 3 g/dL); repeat SPEP in 6 months, then yearly if stable
IgM spike with blurred vision, headache, nosebleeds, engorged retinal veins → Waldenström macroglobulinemia with hyperviscosity; urgent plasmapheresis
High hematocrit, low EPO, itching after hot showers, JAK2 mutation → polycythemia vera; phlebotomy to hematocrit under 45% plus low-dose aspirin
Polycythemia vera at age ≥60 or after a clot → add cytoreduction with hydroxyurea
High hematocrit with normal or high EPO → secondary cause: smoking, sleep apnea, lung disease, testosterone, SGLT2 inhibitor, kidney tumor
Platelets above 450,000 persistently, no iron deficiency or inflammation → test JAK2, CALR, MPL for essential thrombocythemia; aspirin; hydroxyurea if high risk
Older adult with cytopenias, macrocytosis and dysplastic cells → myelodysplastic syndrome; marrow biopsy; transfusion, ESA or hypomethylating agent by risk
Massive spleen, teardrop cells, dry marrow tap → primary myelofibrosis; JAK inhibitor for symptoms and spleen size
Massive splenomegaly → short list: CML, myelofibrosis, hairy cell leukemia, lymphoma, malaria, visceral leishmaniasis
Low counts with an enlarged spleen in cirrhosis → hypersplenism from portal hypertension; manage the liver disease, not the spleen
Left upper quadrant pain and hypotension after trauma or during mono → splenic rupture; FAST or CT if stable; unstable → splenectomy

Traps that cost points

Starting steroids for an unexplained enlarged node before biopsy→ Steroids shrink lymphoma and can erase the diagnosis; get tissue first.
Ordering fine-needle aspiration for suspected lymphoma→ Classification needs node architecture; request excisional or core needle biopsy.
Treating asymptomatic early-stage CLL to prevent progression→ Early treatment does not improve survival; watch, and treat for symptoms, cytopenias, rapid doubling or bulky nodes.
Waiting for PML-RARA results before starting all-trans retinoic acid→ Most early deaths come from bleeding in the first days; start the drug on clinical suspicion.
Ordering a nuclear bone scan to find myeloma lesions→ Lytic lesions lack osteoblastic activity and are missed; use low-dose whole-body CT, PET-CT or MRI.
Prescribing amoxicillin for a sore throat that turns out to be mono→ It causes a diffuse rash in EBV infection and does not help; confirm strep before antibiotics.
Transfusing red cells to a patient with leukostasis→ More cells raise viscosity further; lower the white count first, transfusing only if essential.
Calling every high hematocrit polycythemia vera→ Check EPO and look for smoking, sleep apnea, testosterone or an SGLT2 inhibitor before a JAK2 workup.