Diagnostic Approach to Iron Deficiency Anemia

Initial Evaluation

The American Gastroenterological Association recommends confirming iron deficiency with serum ferritin, the single most useful marker, before proceeding with investigations to identify the underlying cause, which should include urinalysis, coeliac disease screening, and bidirectional endoscopy in at-risk populations 1, 2
Serum ferritin is the most powerful and specific test for iron deficiency, with ferritin <15 μg/L being diagnostic of absent iron stores, and ferritin <30 μg/L generally indicating low body iron stores 3, 4
The World Health Organization defines anemia as hemoglobin <130 g/L in men, <120 g/L in non-pregnant women, and <110 g/L in pregnant women (2nd/3rd trimester) 4

Transferrin saturation <20-30% supports the diagnosis of iron deficiency anemia when ferritin is equivocal 3, 4
Mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) typically show microcytosis and hypochromia in iron deficiency anemia 4, 5
Red cell distribution width (RDW) may be elevated, particularly in combined deficiencies 3, 5

A hemoglobin rise ≥10 g/L within 2 weeks of iron therapy is highly suggestive of absolute iron deficiency, even when iron studies are equivocal 1, 2, 4
Ferritin <100 μg/L may still indicate iron deficiency in inflammatory states 6

Urinalysis or urine microscopy is recommended to exclude renal tract blood loss 1, 7
Coeliac disease screening is recommended, as it is found in 3-5% of iron deficiency anemia cases 1, 2, 7
Bidirectional endoscopy is the standard investigation for men and postmenopausal women with newly diagnosed iron deficiency anemia 1, 2, 7

If bidirectional endoscopy is negative and iron deficiency anemia persists or recurs despite iron therapy, capsule endoscopy is the preferred test for small bowel examination 1, 2, 7
CT/MR enterography are complementary for inflammatory and neoplastic small bowel disease 1, 2