22nd May 2023

Investigating iron deficiency anaemia

Blood tests commonly used to diagnose iron deficiency anaemia include:

• Full blood count
  • Haemoglobin – low
  • Haematocrit – low
  • MCV – typically low, may be normal
  • MCH – typically low i.e. hypochromic but may be normal
  • Reticulocytes – low or normal
  • RDW– high, due to variability in size of red cells
• Blood film
  • Hypochromic, microcytic red blood cells
  • Poikilocytosis may be seen – target cells and pencil cells are commonly associated with iron deficiency anaemia.
• Iron profile
  • Ferritin – low ferritin is suggestive of iron deficiency; however ferritin is an acute phase reactant and therefore may be normal or elevated if co-existing inflammation.
  • Serum iron – low serum iron may be seen; however, this is not a reliable test in isolation
  • Serum TIBC – increased
  • Transferrin saturation – low (<16%). The percentage transferrin saturation is calculated by serum iron ÷ TIBC x 100.
  • Serum soluble transferrin receptor – increased

Additional investigations to identify a cause may include:

• OGD and colonoscopy – this is particularly important for men and post-menopausal women as occult gastrointestinal cancers are a common cause of iron deficiency anaemia. Small-bowel biopsy can also be undertaken if suspicion of coeliac disease.
• Coeliac serology
• Urinalysis – to investigate occult blood loss from the renal tract
• Helicobacter pylori testing
• Stool sample for ova and parasites if suspicion of hookworm infection
• Gynaecology workup for menorrhagia