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Laboratory medicine in primary care: Investigating iron status in microcytic anaemia

BMJ 2007; 334 doi: (Published 01 May 2007) Cite this as: BMJ 2007;334:0705183
  1. Michael J Galloway, haematologist1,
  2. W Stuart A Smellie, chemical pathologist2
  1. 1City Hospitals Sunderland, NHS Foundation Trust, Sunderland Royal Hospital, Sunderland SR4 7TP
  2. 2Clinical Laboratory, General Hospital, Bishop Auckland DL14 6AD

Microcytic anaemia is often assumed to indicate iron deficiency, but up to 20-30% of patients will have another diagnosis. Measurement of serum ferritin offers the best means of confirming iron deficiency, say Michael J Galloway and W Stuart A Smellie

The investigation of possible iron deficiency has changed in recent years. Traditionally, measurements of iron and iron binding capacity were performed by laboratories, but serum ferritin has now become established as a more reliable test for iron deficiency, although results in both situations can be influenced by the presence of acute or chronic inflammation.

In populations in which the prevalence of haemoglobinopathy genes is low, the finding of a microcytic anaemia is considered by some to be sufficient to indicate iron deficiency anaemia. However, this can lead to an erroneous diagnosis, as shown in the cases below.

Case 1

A 69 year old man was referred for investigation of iron deficiency anaemia. History revealed that he had been feeling generally tired for two months and had lost 6 kg in weight. His haemoglobin concentration had not increased despite taking ferrous sulphate 200 mg thrice daily for eight weeks. Full blood count taken in primary care had shown haemoglobin 95 g/l, mean cell volume 73 fl, white cell count 7.5×109/l, and platelets 480×109/l. Subsequent investigations in secondary care also showed an erythrocyte sedimentation rate of 80 mm in the first hour and a ferritin concentration of 577 µg/l, and these high values indicated that the diagnosis was anaemia of chronic inflammation (chronic disease). Subsequent computed tomography revealed the presence of a renal carcinoma in the left kidney, and the patient was therefore referred for surgical removal of the tumour.

Case 2

A 75 year old woman had been investigated for what was thought to be iron deficiency due to chronic gastrointestinal …

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