What additional laboratory tests should I order to determine the type and cause of anemia?

Additional Laboratory Tests for Anemia Evaluation

Based on the low MCH, MCHC, and high RDW values, you should order serum ferritin, transferrin saturation (TSAT), reticulocyte count, and serum vitamin B12 and folate levels to determine the type and cause of anemia. 1

Initial Findings Analysis

• Your patient's CBC shows low MCH (25.6 pg) and MCHC (29.4 g/dL), suggesting hypochromic anemia, most commonly associated with iron deficiency 1
• The elevated RDW (17.2%) indicates anisocytosis (variation in red cell size), which is consistent with iron deficiency anemia but requires further confirmation 1, 2

Recommended Laboratory Tests

First-Line Tests

• Serum ferritin: Most useful single marker of iron deficiency; levels <30 μg/L in patients without inflammation confirm iron deficiency 1
• Transferrin saturation (TSAT): Helps identify iron availability for erythropoiesis; particularly useful when ferritin results may be falsely normal due to inflammation 1
• Absolute reticulocyte count: Essential to assess bone marrow response to anemia; low counts suggest inadequate production (common in iron deficiency) 3, 1

Additional Tests

• Serum vitamin B12 and folate levels: To rule out deficiencies that may contribute to or cause anemia 1
• C-reactive protein (CRP): To assess for inflammation that might affect ferritin interpretation 1
• Peripheral blood smear: To evaluate red cell morphology and confirm microcytosis/hypochromia 1, 2

Interpretation Guidelines

Iron Deficiency Diagnosis

• Definitive diagnosis: Serum ferritin <30 μg/L without inflammation 1
• In presence of inflammation: Ferritin up to 100 μg/L may still indicate iron deficiency 1
• Combined deficiency: If ferritin is between 30-100 μg/L, a combination of true iron deficiency and anemia of chronic disease is likely 1

Reticulocyte Count Interpretation

• Low or normal reticulocyte count in an anemic patient suggests inadequate bone marrow response, consistent with iron deficiency 3, 1
• The reticulocyte index (corrected for degree of anemia) provides more accurate assessment of bone marrow production capacity 3, 4

Clinical Pitfalls to Avoid

• Relying solely on hemoglobin and hematocrit: These decrease only in severe iron depletion and can miss early iron deficiency 2
• Not measuring iron parameters: CBC alone without iron studies may lead to missed diagnoses of iron depletion 2
• Misinterpreting normal ferritin: In inflammatory states, ferritin may be falsely normal or elevated despite iron deficiency 1
• Overlooking combined deficiencies: Multiple nutritional deficiencies can coexist and require comprehensive evaluation 5, 6

Follow-up Testing

• Consider reticulocyte hemoglobin content (CHr) if available, as it's an early marker of iron-deficient erythropoiesis and less affected by inflammation 7
• If iron deficiency is confirmed but unexplained, further investigation for sources of blood loss may be warranted, especially in non-menstruating patients 1

By following this systematic approach to laboratory testing, you'll be able to accurately determine the type and cause of anemia in your patient, enabling appropriate treatment planning.