What labs should be ordered for a patient suspected of having iron deficiency anemia?

Laboratory Testing for Iron Deficiency Anemia

Order hemoglobin/hematocrit and serum ferritin as your initial diagnostic tests, with ferritin <45 ng/mL plus hemoglobin <13 g/dL in men or <12 g/dL in non-pregnant women confirming iron deficiency anemia. 1

Essential First-Line Tests

The diagnostic workup should begin with these core laboratory tests:

• Complete blood count (CBC) with hemoglobin/hematocrit to establish anemia, using thresholds of <13 g/dL in men, <12 g/dL in non-pregnant women, and <11 g/dL in pregnant women 1, 2

• Serum ferritin as the most specific single test for iron deficiency, with <15 µg/L indicating absent iron stores and <45 ng/mL being the optimal diagnostic threshold when combined with anemia criteria 1

• Red cell indices including mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and red cell distribution width (RDW) provide supporting evidence for iron deficiency 1

Second-Line Tests for Equivocal Cases

When ferritin results are borderline or inflammatory conditions are present, add these tests:

• Transferrin saturation (calculated as serum iron/total iron binding capacity × 100), with <20% indicating iron deficiency and <30% supporting diagnosis when ferritin is equivocal 1, 3

• C-reactive protein (CRP) to interpret ferritin in inflammatory states, since ferritin is an acute phase reactant and may be falsely elevated in inflammation 1

• Serum transferrin receptor (sTfR) to distinguish between iron deficiency and anemia of chronic disease, particularly useful in patients with chronic inflammatory conditions 1

Additional Specialized Tests

For specific clinical scenarios, consider:

• Percentage of hypochromic red cells >2.5% suggests iron deficiency, particularly useful in chronic kidney disease patients 1

• Reticulocyte hemoglobin concentration as an index of iron-deficient erythropoiesis 4

Important Diagnostic Caveats

Ferritin interpretation requires clinical context. In patients without inflammatory conditions, use <30 ng/mL as the diagnostic cutoff 3. However, ferritin may be falsely elevated in infectious, inflammatory, and neoplastic conditions, requiring additional testing with transferrin saturation or sTfR 1, 5

A therapeutic trial of oral iron can serve as both diagnostic and confirmatory test, with a hemoglobin rise ≥10 g/L within 2 weeks strongly suggesting absolute iron deficiency 1, 2

Monitoring After Diagnosis

• Target ferritin >100 ng/mL to confirm iron store restoration 1

• Continue hemoglobin monitoring after resolution of anemia to ensure sustained response 1