What are the diagnostic tests and management for suspected hemolysis?

Diagnostic Tests and Management for Suspected Hemolysis

When hemolysis is suspected, immediately order a complete blood count with reticulocyte count, peripheral blood smear, lactate dehydrogenase (LDH), haptoglobin, indirect bilirubin, and direct antiglobulin test (DAT/Coombs) to confirm hemolysis and differentiate immune from non-immune causes. 1, 2

Initial Diagnostic Workup

First-Line Laboratory Tests

• Complete blood count (CBC) with differential and reticulocyte count to assess anemia severity and confirm bone marrow response (reticulocyte count >3-5% indicates increased red cell turnover) 1, 3, 2
• Peripheral blood smear examination is mandatory to identify morphologic abnormalities such as schistocytes, spherocytes, or other diagnostic red cell changes 1, 2
• Lactate dehydrogenase (LDH) - elevated levels confirm tissue destruction and hemolysis 1, 3, 2
• Haptoglobin - decreased levels indicate intravascular hemolysis as haptoglobin binds free hemoglobin 1, 3, 2
• Total and indirect (unconjugated) bilirubin - elevated indirect bilirubin reflects increased red cell breakdown 1, 3, 4
• Direct antiglobulin test (DAT/Coombs test) - this critical test distinguishes immune-mediated hemolysis (positive) from non-immune causes (negative) 1, 3, 2

Additional Markers for Severe Intravascular Hemolysis

• Plasma free hemoglobin - elevated in severe intravascular hemolysis; levels >1.4 g/L indicate clinically significant hemolysis 5
• Hemoglobinuria and hemosiderinuria - occur only with severe, rapid intravascular hemolysis 4, 2
• Hemopexin - decreased levels indicate consumption during hemoglobin clearance 4

Critical Diagnostic Considerations

Thrombotic Microangiopathy (TMA) Evaluation

If schistocytes are present on blood smear, immediately order ADAMTS13 activity level and inhibitor titer, as this represents a medical emergency requiring urgent plasma exchange if thrombotic thrombocytopenic purpura (TTP) is confirmed. 6, 1

• ADAMTS13 activity and inhibitor titer - levels <10% indicate TTP; levels >10% suggest atypical hemolytic uremic syndrome (aHUS) 6
• Complement testing (C3, C4, CH50) for suspected complement-mediated HUS 6, 3
• Creatinine and urinalysis to assess renal involvement 6
• Do not delay plasma exchange while awaiting ADAMTS13 results if TTP is strongly suspected clinically, as mortality increases with treatment delay 6, 1

Neonatal Hemolysis Workup

• Fractionated bilirubin, maternal and infant blood typing, and DAT are essential in neonates with jaundice 3
• G6PD enzyme assay should be performed in infants of African, Mediterranean, or Asian descent if initial tests are inconclusive 3
• End-tidal carbon monoxide corrected for ambient CO (ETCOc) provides direct measurement of heme catabolism rate and is more specific than standard hemolysis markers, though its impact on management remains unclear 7, 3

Management Algorithm

Grade 1-2 (Mild to Moderate Hemolysis)

• Hold any potentially causative medications and obtain hematology consultation 7, 1
• Administer prednisone 0.5-1 mg/kg/day for autoimmune hemolytic anemia 7, 6, 1
• Folic acid 1 mg daily to support erythropoiesis 1
• Monitor hemoglobin levels weekly during steroid tapering 6

Grade 3 (Severe Hemolysis with Clinical Consequences)

• Consider hospital admission based on clinical judgment 7, 6
• Increase prednisone to 1-2 mg/kg/day 7, 6
• RBC transfusion only to relieve symptoms or achieve hemoglobin 7-8 g/dL in stable, non-cardiac patients 7, 6, 1
• Use extended antigen-matched red cells (C/c, E/e, K, Jk^a^/Jk^b^, Fy^a^/Fy^b^, S/s) if alloimmunization is suspected 6

Grade 4 (Life-Threatening Hemolysis)

For TTP (ADAMTS13 <10%):

• Immediately initiate therapeutic plasma exchange (PEX) according to existing guidelines 7, 6, 1
• Administer methylprednisolone 1g IV daily for 3 days, with first dose typically given immediately after first PEX 7, 6
• Platelet transfusion is contraindicated except for life-threatening bleeding 6, 1
• Consider rituximab for refractory cases 6

For aHUS (ADAMTS13 >10% with complement activation):

• Begin eculizumab therapy: 900 mg weekly for four doses, 1,200 mg week 5, then 1,200 mg every 2 weeks 7, 6, 1
• Administer meningococcal vaccination and long-term penicillin prophylaxis 7

Common Pitfalls and Caveats

• Standard laboratory tests for hemolysis have poor specificity and sensitivity and are frequently unhelpful in isolation 7
• Low schistocyte counts do not exclude TMA due to low test sensitivity; absence of abundant schistocytes should not delay evaluation 6
• Proper specimen handling is crucial - use straight needle rather than butterfly, avoid tourniquet pressure, and process samples within 1 hour at room temperature to prevent in vitro hemolysis 3
• Visibly hemolyzed samples should be rejected as they cause spurious results in more than 60% of cases 3, 8
• Review medication history thoroughly as drug-induced hemolysis is common and reversible 1, 2
• Malignant hypertension can cause TMA with only moderate thrombocytopenia and few schistocytes; check blood pressure and perform funduscopic examination 6