How is hemolysis diagnosed and treated?

How to Determine Hemolysis

Hemolysis is diagnosed by demonstrating increased red blood cell destruction through a combination of laboratory markers: elevated reticulocyte count, increased lactate dehydrogenase (LDH), decreased haptoglobin, elevated unconjugated bilirubin, and characteristic findings on peripheral blood smear. 1, 2

Initial Laboratory Workup

The minimum essential tests to confirm hemolysis include:

• Complete blood count (CBC) with red cell indices (MCV, RDW) to assess anemia severity and red cell characteristics 1
• Reticulocyte count: Elevated reticulocytes (>3-5%) indicate increased red cell turnover and appropriate bone marrow response to hemolysis 1, 3, 2
• Lactate dehydrogenase (LDH): Markedly elevated in hemolysis due to release from lysed red cells 1, 3, 2
• Haptoglobin: Decreased or undetectable, as it binds free hemoglobin released during hemolysis 1, 3, 2
• Unconjugated (indirect) bilirubin: Elevated due to increased heme catabolism, typically <5 mg/dL in chronic hemolysis 1, 2
• Peripheral blood smear: Essential to identify red cell morphology abnormalities (spherocytes, schistocytes, sickle cells, bite cells) that suggest specific etiologies 1, 2

Distinguishing Intravascular from Extravascular Hemolysis

For intravascular hemolysis specifically, additional markers include:

• Hemoglobinemia: Free hemoglobin in plasma 4, 2
• Hemoglobinuria: Dark or red-tinged urine from filtered hemoglobin 1, 4, 2
• Hemosiderinuria: Iron deposits in urine sediment from chronic intravascular hemolysis 4

These findings occur only with severe, rapid intravascular hemolysis (incompatible transfusion, G6PD deficiency crisis, paroxysmal nocturnal hemoglobinuria) 4.

Critical Next Step: Direct Antiglobulin Test (DAT)

The direct antiglobulin test (Coombs test) is mandatory to differentiate immune-mediated from non-immune hemolysis 1, 3, 2, 5:

• Positive DAT: Indicates immune-mediated hemolysis (autoimmune hemolytic anemia, transfusion reactions, drug-induced)
• Negative DAT: Points toward non-immune causes (hereditary spherocytosis, G6PD deficiency, membrane defects, enzymopathies, microangiopathic hemolysis)

Common Pitfall: Reticulocyte Count Interpretation

A "normal" or low reticulocyte count in the presence of anemia does NOT exclude hemolysis—it indicates inability to respond appropriately due to nutritional deficiencies (iron, B12, folate), bone marrow disease, or splenic sequestration of young red cells 1. In pyruvate kinase deficiency, reticulocytosis may be disproportionately low relative to hemolysis severity due to selective splenic trapping of younger PK-deficient cells 1.

Extended Workup for Unclear Cases

When initial testing confirms hemolysis but the etiology remains unclear, proceed with:

• Vitamin B12 and folate levels: Macrocytosis may indicate deficiency 1
• Serum ferritin and transferrin saturation: To assess iron status, particularly in inflammatory bowel disease patients 1
• G6PD enzyme assay: Especially in patients of African, Mediterranean, or Asian descent 3
• Hemoglobin electrophoresis: To identify hemoglobinopathies (sickle cell disease, thalassemia) 5
• Osmotic fragility test: For hereditary spherocytosis, though can be normal or altered 1
• Red cell enzyme assays: Pyruvate kinase activity measurement if enzymopathy suspected 1

Specialized Testing for Thrombotic Microangiopathy

If schistocytes are present on smear, immediately order ADAMTS13 activity level and inhibitor titer to distinguish thrombotic thrombocytopenic purpura (TTP) from other thrombotic microangiopathies 6:

• ADAMTS13 <10%: Diagnostic of TTP, requires immediate plasma exchange 6
• ADAMTS13 >10%: Consider atypical hemolytic uremic syndrome (aHUS), complement testing (C3, C4, CH50), and other causes 6

Critical pitfall: Do not dismiss TMA based on "rare" schistocytes alone—low schistocyte counts can occur in early or evolving disease 6. The absence of abundant schistocytes does not exclude TMA due to low test sensitivity 6.

Neonatal Hemolysis Considerations

For suspected hemolytic jaundice in neonates, obtain:

• Fractionated bilirubin to confirm predominantly unconjugated hyperbilirubinemia 3
• Maternal and infant blood typing (ABO, Rh) to identify incompatibility 3
• Direct antiglobulin test on infant blood 3
• End-tidal carbon monoxide (ETCOc): Provides direct assessment of heme catabolism rate with better specificity than standard markers 3

Sample Quality Considerations

Proper specimen handling is crucial to avoid false results from in vitro hemolysis 3:

• Use a straight needle rather than butterfly to minimize hemolysis
• Avoid excessive tourniquet pressure during collection
• Process samples within 1 hour at room temperature
• Reject visibly hemolyzed samples as they cause spurious results in >60% of cases 3

Monitoring During Acute Hemolysis

For patients with confirmed hemolysis requiring treatment, monitor:

• Daily CBC with differential, LDH, haptoglobin, and creatinine during acute phase 6
• Serial bilirubin measurements within 2-3 hours if total serum bilirubin ≥25 mg/dL or rapidly rising 3
• Reticulocyte count to assess bone marrow response 1