What laboratory tests should be ordered to evaluate a patient with suspected hemolysis?

Laboratory Workup for Suspected Hemolysis

When evaluating a patient with suspected hemolysis, order a complete blood count with peripheral smear, reticulocyte count, lactate dehydrogenase, haptoglobin, direct and indirect bilirubin, and direct antiglobulin test (Coombs test) as the essential initial panel. 1, 2

Core Initial Laboratory Tests

The following tests establish the presence and mechanism of hemolysis:

Essential Hemolysis Markers

• Complete blood count (CBC) to assess for anemia and macrocytosis 2, 1
• Peripheral blood smear to identify spherocytes, schistocytes, agglutination, and other morphologic abnormalities that can be diagnostic 2, 1, 3, 4
• Reticulocyte count to evaluate bone marrow compensatory response (typically elevated in hemolysis) 2, 1, 3, 4
• Lactate dehydrogenase (LDH) which is elevated due to red cell destruction 2, 1, 3, 4
• Haptoglobin which is decreased in intravascular hemolysis 2, 1, 3, 4
• Direct and indirect bilirubin to document unconjugated (indirect) hyperbilirubinemia 2, 1, 3, 4

Critical Immunohematologic Testing

• Direct antiglobulin test (DAT/Coombs test) is the cornerstone test that differentiates immune-mediated from non-immune hemolysis by detecting IgG and/or C3d coating on red blood cells 2, 1, 3, 4

Secondary Evaluation for Etiology

Once hemolysis is confirmed, pursue these tests to identify the underlying cause:

Immune and Infectious Workup

• Autoimmune serology to identify specific autoantibodies 2, 1
• Viral studies including CMV, EBV, HHV6, and parvovirus 2
• Bacterial cultures including mycoplasma and other infectious causes 2, 1

Hereditary and Enzymatic Causes

• Glucose-6-phosphate dehydrogenase (G6PD) level to exclude enzymatic hemolysis, particularly in patients with oxidative stress exposure 2, 1, 3
• Hemoglobin electrophoresis if hemoglobinopathy (sickle cell, thalassemia) is suspected 3

Specialized Testing Based on Clinical Context

• Paroxysmal nocturnal hemoglobinuria (PNH) screening by flow cytometry to evaluate loss of GPI-anchored proteins 2, 1
• Protein electrophoresis and cryoglobulin analysis to evaluate for lymphoproliferative disorders 2, 1
• Disseminated intravascular coagulation (DIC) panel including PT/INR and PTT if DIC is suspected 2, 1
• Free hemoglobin in cases of suspected intravascular hemolysis 2
• Methemoglobinemia assessment when clinically indicated 2, 1

Additional Supportive Tests

Metabolic and Nutritional Assessment

• Blood chemistry panel including creatinine to assess for acute kidney injury from hemoglobinuria 1
• Vitamin B12, folate, copper, and iron studies if bone marrow failure syndrome is suspected or refractory cases 2
• Homocysteine or methylmalonic acid (MMA) for nutritional causes of macrocytosis 2

Advanced Testing for Complex Cases

• Bone marrow aspiration and biopsy with cytogenetic analysis if no obvious cause is identified or to evaluate for myelodysplastic syndromes 2, 1
• ADAMTS13 activity level to rule out thrombotic thrombocytopenic purpura (TTP) if schistocytes are present 2
• Complement testing (C3, C4, CH50) for suspected complement-mediated hemolysis 2

Critical Pitfalls to Avoid

Medication History is Essential

Always obtain a detailed medication history as numerous drugs cause hemolysis including ribavirin, rifampin, dapsone, interferon, cephalosporins, penicillins, NSAIDs, quinine/quinidine, fludarabine, ciprofloxacin, lorazepam, diclofenac, tacrolimus, cyclosporine, and sirolimus 2, 1

Transfusion Timing Matters

Recent blood transfusions can falsely normalize enzyme activity assays and interfere with antibody testing, so always document transfusion history 2

High-Risk Populations Require Special Attention

Patients with chronic lymphocytic leukemia, non-Hodgkin's lymphoma, or autoimmune disease have higher risk of autoimmune hemolytic anemia and warrant lower threshold for Coombs testing 1

Blood Bank Coordination

Coordinate with the blood bank before transfusions in suspected immune-mediated hemolysis to ensure appropriate crossmatching and minimize transfusion reactions 1

Reticulocyte Count Can Be Misleading

Markedly elevated reticulocyte counts can falsely normalize pyruvate kinase enzyme activity assays, and incomplete platelet/leukocyte removal can interfere with results 2