What labs do you order for iron deficiency?

Laboratory Tests for Iron Deficiency

Serum ferritin is the most specific test for iron deficiency and should be ordered along with complete blood count, transferrin saturation, and screening for celiac disease when evaluating for iron deficiency. 1, 2

Core Laboratory Panel for Iron Deficiency

• Complete Blood Count (CBC)

  • Hemoglobin and hematocrit
  • Red cell indices (MCV, MCH, MCHC)
  • Red cell distribution width (RDW)
  • Red blood cell count

• Iron Studies

  • Serum ferritin (primary test for iron stores)
  • Serum iron
  • Total iron binding capacity (TIBC)
  • Transferrin saturation (calculated as: serum iron/TIBC × 100)

• Celiac Disease Screening

  • Tissue transglutaminase (TTG) antibodies 1

Interpretation of Results

Serum Ferritin

• <15 μg/L: Confirms iron deficiency with high specificity (98-100%) 1, 2
• 15-30 μg/L: Suggestive of iron deficiency
• <45 μg/L: May warrant further investigation 2
• In inflammatory states: Values up to 100 μg/L may still indicate iron deficiency 2

Transferrin Saturation

• <20%: Suggests iron deficiency 2
• <30%: May help confirm diagnosis in borderline cases 1

CBC Patterns

• Microcytic (low MCV), hypochromic (low MCH) anemia with elevated RDW (>14%): Characteristic of iron deficiency 1, 2
• Low MCV with normal RDW (≤14%): Consider thalassemia 1

Important Considerations

1. Ferritin as an acute-phase reactant: Ferritin levels can be falsely elevated in inflammatory conditions, infections, or liver disease, masking iron deficiency 1, 2

2. Isolated CBC without iron studies: Many cases of iron deficiency may be missed if only CBC is ordered without iron studies 3

3. Special populations:

   • Pregnant women: May need higher ferritin cutoffs
   • Patients with chronic inflammatory diseases: Consider using higher ferritin cutoffs (up to 100 μg/L) 2
   • Elderly patients: May have multiple causes of anemia

4. IgA deficiency: Can cause false-negative TTG results when screening for celiac disease 1

5. Timing of blood draws: Serum iron has diurnal variation with higher levels in the morning 1

Pitfalls to Avoid

• Relying solely on hemoglobin and hematocrit to diagnose iron deficiency - these parameters decrease only in severe iron depletion 3

• Accepting a normal MCV as evidence against iron deficiency - early iron deficiency may present with normal MCV 3

• Failing to screen for celiac disease in unexplained iron deficiency - present in 2-3% of patients with iron deficiency anemia 1, 2

• Neglecting to check iron studies in patients with normal hemoglobin - iron deficiency without anemia can still cause symptoms like fatigue and reduced exercise capacity 4

• Accepting ferritin values in the "normal" range during inflammation - consider the clinical context when interpreting results 2

By following this comprehensive laboratory approach to diagnosing iron deficiency, clinicians can identify patients early in the disease process before anemia develops and address both the iron deficiency and its underlying cause.