[Iron deficiency anaemia--interpretation of biochemical and haematological findings].

BACKGROUND: Iron deficiency and iron deficiency anaemia are frequent problems in both the primary and the specialist health services. It is important to detect iron deficiency and to determine the causal relationship because iron deficiency may be secondary to a serious disease. The diagnosis of iron deficiency is largely based on biochemical and haematological laboratory findings, but there is no standardisation or consensus on the interpretation of these findings. METHOD: Non-systematic search in the PubMed database with a discretionary selection of articles, based on the authors' knowledge of the field. RESULTS: Ferritin measurement is the most important analysis in the study of iron deficiency, but there is no consensus on the diagnostic cut-off. It is usual in Norway today to use a ferritin level of < 12-20 μg/L, but at this low level the sensitivity for detecting iron deficiency is very low. A number of studies show that if the diagnostic cut-off is increased to the order of 30 μg/L the sensitivity is significantly higher for only a small reduction in specificity. INTERPRETATION: When studying iron deficiency as a cause of anaemia, the diagnostic cut-off for detecting deficiency should be higher than that used today. The ferritin level increases with inflammation and ought in practice to be considered in conjunction with the CRP level. The level of transferrin receptor in plasma increases with iron deficiency without being influenced by inflammation and is therefore a good supplement to ferritin measurement. Measurement of iron, transferrin and transferrin saturation provides little information additional to that provided by ferritin in iron deficiency studies.