About This Page
This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Hemolysis labs: high reticulocytes, high LDH, high indirect bilirubin, low haptoglobin
- Direct antiglobulin test identifies immune hemolysis; warm AIHA is usually IgG and extravascular
- Schistocytes indicate microangiopathic hemolytic anemia such as TTP, HUS, DIC, HELLP, or mechanical valve hemolysis
- Spherocytes occur in warm autoimmune hemolysis and hereditary spherocytosis
- The most urgent Step 2 CK task is recognizing TTP and starting plasma exchange without waiting for ADAMTS13
Overview
Hemolytic anemia is a pattern rather than a single diagnosis. RBC destruction may be intravascular, with hemoglobinuria and markedly low haptoglobin, or extravascular, with splenic and hepatic macrophage clearance. The peripheral smear directs the differential: schistocytes suggest mechanical fragmentation; spherocytes suggest membrane loss or immune-mediated removal; bite cells suggest oxidative injury; sickled cells suggest sickle cell disease.
Epidemiology
Hemolytic anemia can occur at any age. Common acquired causes include autoimmune hemolytic anemia, drugs, infections, DIC, TTP, HUS, mechanical valves, and transfusion reactions. Inherited causes include sickle cell disease, thalassemia, G6PD deficiency, hereditary spherocytosis, and pyruvate kinase deficiency.
Clinical Features
Symptoms
Fatigue, dyspnea, jaundice, dark urine
Back pain or abdominal pain in acute intravascular hemolysis
Fever, neurologic symptoms, renal failure, or thrombocytopenia suggesting TTP/HUS/DIC
Recent medication, infection, transfusion, pregnancy, or autoimmune disease history
Signs
Jaundice, pallor, tachycardia
Splenomegaly in extravascular hemolysis
Petechiae or bleeding if thrombocytopenia or DIC is present
Hypertension or edema with renal injury in HUS/TTP
Investigations
First-line
CBC, reticulocyte count, smearReticulocytosis if marrow response intact; smear pattern is central
Hemolysis labsLDH high, indirect bilirubin high, haptoglobin low; hemoglobinuria suggests intravascular hemolysis
Direct antiglobulin test (Coombs)Positive in autoimmune hemolysis; negative in MAHA, G6PD, hereditary hemolysis
Second-line
Coagulation profilePT/aPTT/fibrinogen/D-dimer to evaluate DIC; coagulation tests are usually normal in TTP/HUS
Creatinine and urinalysisRenal injury suggests HUS, TTP, severe intravascular hemolysis, or DIC
Medication and infection testingEvaluate drug-induced hemolysis, Mycoplasma, EBV, HIV, hepatitis, malaria risk, or tickborne disease as appropriate
Specialist
ADAMTS13 activitySupports TTP diagnosis but treatment should not wait when clinical suspicion is high
Complement and genetic testingConsider atypical HUS or complement-mediated hemolysis under specialist care
1
Initial stabilization
- Assess hemodynamic stability and transfuse if severe symptomatic anemia
- Stop suspected causative drugs and treat infection or trigger
- Involve hematology early when schistocytes, thrombocytopenia, renal injury, or neurologic symptoms are present
2
Immune hemolysis
- Warm AIHA: corticosteroids first-line; rituximab or splenectomy for refractory disease
- Cold agglutinin disease: avoid cold exposure; rituximab-based therapy for symptomatic disease
- Transfuse when necessary despite compatibility challenges
3
Microangiopathic hemolysis
- TTP: immediate plasma exchange plus corticosteroids; add caplacizumab/rituximab in many modern protocols
- HUS: supportive care; eculizumab/ravulizumab for atypical complement-mediated HUS
- DIC: treat underlying cause and support coagulation with platelets, cryoprecipitate, FFP when bleeding or procedures require it
Complications
- Hemodynamic collapse: Severe acute hemolysis can cause shock and ischemia
- Pigment gallstones: Chronic extravascular hemolysis
- Acute kidney injury: Hemoglobinuria or thrombotic microangiopathy
- Missed TTP: Fatal if plasma exchange is delayed
USMLE Step 2 CK Exam Tips
- 1Schistocytes + thrombocytopenia = thrombotic microangiopathy until proven otherwise
- 2TTP has normal PT/aPTT; DIC has prolonged PT/aPTT and low fibrinogen
- 3Warm AIHA: IgG, positive Coombs, spherocytes, splenomegaly
- 4Cold agglutinin disease: IgM, complement-mediated, acrocyanosis after cold exposure
- 5Bite cells = G6PD deficiency; sickled cells = sickle cell disease
- 6Do not wait for ADAMTS13 to treat suspected TTP
practicetest your knowledge on hemolytic anemiasApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — hematology & oncology and beyond.
open q-bank