What labs should I order for a patient with anemia?

Laboratory Tests for Anemia Evaluation

The essential laboratory tests for a patient with anemia should include complete blood count (CBC), iron studies (serum ferritin, transferrin saturation), vitamin B12, and folate levels to determine the underlying cause and guide appropriate treatment. 1, 2

Initial Laboratory Evaluation

• Complete Blood Count (CBC) with differential to assess hemoglobin level, red blood cell indices (MCV, MCH, MCHC), and reticulocyte count 1, 2
• Serum ferritin - the most useful single marker of iron deficiency, with levels <30 μg/L confirming iron deficiency in patients without inflammation 2
• Transferrin saturation (TSAT) - helps identify iron availability for erythropoiesis, particularly useful when ferritin results may be affected by inflammation 1, 2
• Serum iron and Total Iron Binding Capacity (TIBC) - reflects amount of iron immediately available for hemoglobin synthesis 1
• Vitamin B12 and folate levels - to rule out deficiencies that may contribute to or cause anemia 1, 2
• Reticulocyte count - to evaluate bone marrow response to anemia 1

Additional Tests Based on Clinical Context

• For suspected iron deficiency anemia:

  • Stool guaiac test for occult blood to evaluate for gastrointestinal bleeding 1
  • If ferritin is between 30-100 μg/L with suspected inflammation, consider additional testing as this may still indicate iron deficiency 2

• For patients with chronic kidney disease:

  • Consider percent hypochromic red blood cells (PHRBC) and content of hemoglobin in red blood cells (CHr) if available 1

• For cancer patients with anemia:

  • Consider testing for hemolysis with Coombs test in patients with chronic lymphocytic leukemia, non-Hodgkin lymphoma, or history of autoimmune disease 1
  • Endogenous erythropoietin (EPO) concentrations may predict response in patients with myelodysplasia 1

Interpretation Guidelines

• Iron deficiency anemia is confirmed with:

  • Hemoglobin <13 g/dL in men or <12 g/dL in non-pregnant women, AND
  • Ferritin <45 ng/mL 1

• In patients with inflammation, ferritin up to 100 μg/L may still indicate iron deficiency 2

• Normal ranges for iron markers in non-dialysis CKD patients:

  • Ferritin levels <25 ng/mL in males and <11 ng/mL in females predict insufficient iron stores 1
  • TSAT <16% indicates absolute iron deficiency in general population 1

Follow-up Testing

• If initial tests reveal iron deficiency but the cause is unclear, especially in non-menstruating patients, further investigation for sources of blood loss is warranted 1, 2

• In patients with unexplained anemia after initial workup, consider:

  • Bone marrow examination if abnormalities in multiple cell lines are present 1
  • Endoscopic evaluation (particularly in men and post-menopausal women) 1
  • Testing for less common causes of anemia based on clinical suspicion 3

Common Pitfalls to Avoid

• Relying solely on hemoglobin and hematocrit without measuring iron status indicators can miss early iron depletion 3
• Misinterpreting normal ferritin in inflammatory states, which may be falsely elevated despite iron deficiency 2
• Failing to consider timing of hemoglobin measurements in hemodialysis patients (predialysis levels are preferred) 1
• Not adjusting ferritin interpretation in the context of inflammation or chronic kidney disease 1

By following this comprehensive laboratory evaluation approach, you can accurately diagnose the type and cause of anemia, leading to appropriate treatment strategies and improved patient outcomes.