Colorimetric measurement of iron in plasma samples anticoagulated with EDTA.

AIMS To determine if the iron in EDTA anticoagulated plasma samples can be measured by colorimetric assays using Ferrozine. METHODS Paired samples of serum and EDTA plasma were obtained from 24 patients and analysed by three commercial iron methods. The EDTA plasmas were also analysed using methods modified by the addition of zinc sulphate or with different concentrations of Ferrozine. The iron contamination of EDTA sample tubes was measured by atomic absorption spectroscopy. RESULTS Two commercial colorimetric iron methods gave results of zero for EDTA plasma samples. A third commercial reagent gave plasma results that were about 30% lower than their corresponding serum samples. Addition of 7 mmol/l zinc sulphate to this reagent system and extending the sample preincubation time to 300 seconds yielded comparable results from paired serum and EDTA plasma samples. Linear regression analysis gave a slope of 0.97 with an intercept of 0.60 mumol/l and R2 = 0.9943. Measurements by atomic absorption spectroscopy showed that this positive intercept was due to contamination of the blood collection tubes with about 90 ng of iron. CONCLUSIONS Modification of commercial colorimetric iron methods permits the biochemical assessment of iron status and a full blood count from a single EDTA anticoagulated blood sample.