What are the initial laboratory tests for suspected iron deficiency anemia?

Initial Laboratory Tests for Suspected Iron Deficiency Anemia

The initial laboratory tests for suspected iron deficiency anemia should include hemoglobin concentration, hematocrit, complete blood count with red cell indices (MCV, MCH, MCHC, RDW), serum ferritin, transferrin saturation, and screening for celiac disease. 1

Core Laboratory Panel

First-line Tests

• Complete Blood Count (CBC)
  • Hemoglobin (Hb) and hematocrit (Hct)
  • Red cell indices:
    • Mean corpuscular volume (MCV)
    • Mean corpuscular hemoglobin (MCH)
    • Mean corpuscular hemoglobin concentration (MCHC)
    • Red cell distribution width (RDW)

Iron Status Assessment

• Serum ferritin - most specific test for iron deficiency 1

  • <15 μg/L is highly specific for iron deficiency (specificity 0.99)
  • <45 μg/L has good specificity (0.92) and may warrant further investigation
  • In presence of inflammation, values up to 100 μg/L may still indicate iron deficiency 1

• Transferrin saturation (serum iron/total iron binding capacity × 100)

  • <20% suggests iron deficiency 1
  • Calculated from serum iron and total iron binding capacity (TIBC)

Additional Tests

• Celiac disease screening - found in 3-5% of IDA cases 1
  • Serological testing or small bowel biopsy during gastroscopy

Interpretation of Results

Characteristic Findings in Iron Deficiency

• CBC pattern: Microcytic (low MCV), hypochromic (low MCH) anemia with elevated RDW 1, 2

  • The combination of low MCV with markedly elevated RDW (>14%) is highly characteristic of iron deficiency anemia 2
  • Normal RDW with microcytosis suggests thalassemia rather than iron deficiency 2

• Iron studies interpretation:

  • Serum ferritin <15 μg/L confirms iron deficiency with high specificity 1
  • In inflammatory states, ferritin up to 100 μg/L may still indicate iron deficiency 1
  • Low transferrin saturation (<20%) supports diagnosis of iron deficiency 1

Common Pitfalls to Avoid

1. Relying solely on hemoglobin/hematocrit

   • Changes in Hb and Hct occur only in late stages of iron deficiency 1
   • A patient can have iron deficiency without anemia (non-anemic iron deficiency) 1

2. Misinterpreting ferritin in inflammatory states

   • Ferritin is an acute phase reactant and may be falsely elevated in inflammation 1
   • Consider inflammation markers (CRP/ESR) when interpreting borderline ferritin results

3. Failing to screen for celiac disease

   • Celiac disease is a common cause of iron deficiency and should be routinely screened for 1

4. Overlooking potential serious causes

   • In men and postmenopausal women, iron deficiency anemia warrants GI investigation due to risk of malignancy 1, 3

Special Considerations

• Inflammatory conditions: In patients with chronic inflammatory diseases (IBD, CKD), consider using higher ferritin cutoffs (up to 100 μg/L) to diagnose iron deficiency 1

• Chronic kidney disease: Additional evaluation for EPO deficiency may be needed in patients with CKD 1

• Thalassemia vs. Iron Deficiency: If microcytosis is present with normal RDW, consider hemoglobin electrophoresis to rule out thalassemia 1, 2

By following this systematic approach to laboratory testing for suspected iron deficiency anemia, clinicians can accurately diagnose the condition and identify underlying causes, leading to appropriate treatment and improved patient outcomes.