Soluble transferrin receptors in anaemia of pregnancy.
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Anaemia is one of the most common disorders in pregnancy. The most common cause is iron deficiency. Iron deficiency anaemia is relatively easy to diagnose using a serum ferritin of <15 ng/ml. However, because ferritin is an acute phase reactant, the diagnosis of iron deficiency anaemia in hospitalised or ill patients may be difficult, since serum ferritin may be normal or raised, even in the face of iron deficiency. Soluble transferrin receptor assay (STfR) may be useful in these situations because it reflects the degree of iron requirement in relation to supply, and it is not an acute phase reactant. This study was undertaken to detect subclinical anaemia in pregnant women and to correlate STfR assay with the current diagnostic tests for iron deficiency anaemia. One hundred and fifty-three consenting pregnant women seen at the antenatal clinic at King Edward VIII Hospital (KEH) were recruited. Women on haemantinics, who had renal failure, haemoglinopathy and blood transfusion in the past 3 months, were excluded. An ELISA technique was used for the assay of STfR while standard methodology was used for the other biochemical and haematological assays (FBC, urea, creatinine, c reactive protein and iron studies). One hundred and fifty subjects were included in the final analysis. Seventy-two (48%) had varying degrees of iron deficiency anaemia. In 70% (105) of the samples analysed, serum ferritin and STfR agreed on the presence/absence of iron deficiency anaemia. STfR and S:F were 75% and 86% sensitive; 63% and 82% specific, respectively. The calculated positive and negative predictive values are: STfR 64% and 75%; S:F 84% and 87%; Hb 58% and 57%; mean corpuscular volume 91% and 55%, respectively. Ferritin remains the gold standard for the diagnosis of iron deficiency anaemia. However, because ferritin is an acute phase reactant, soluble transferrin receptor assay may be a better test in ill and hospitalised patients where ferritin may be normal or elevated, despite iron deficiency.