EXPERIENCE WITH ZINC PROTOPORPHYRIN AS A MARKER OF ENDOGENOUS IRON AVAILABILITY IN CHRONIC-HEMODIALYSIS PATIENTS

Background. Ferritin and the percentage of transferrin saturation (TS) are established parameters with which to evaluate endogenous iron ava ilability during treatment of renal anaemia with recombinant human ery thropoietin (rHuEpo). Zinc protoporphyrin (ZPP) has been proposed as a nother valid marker in this setting. Methods. We determined the follow ing parameters in 127 patients, including 117 haemodialysis patients: haemoglobin, erythrocytes, haematocrit, mean corpuscular volume(MCV), iron, ferritin, transferrin saturation and ZPP. Of the patients treate d in a cross-sectional study, 38.5% were treated with rHuEpo; 30.7% wi th intravenous iron; and 13.6% with intravenous iron and rHuEpo simult aneously. Median ferritin was 304 ng/ml and median transferrin saturat ion was 21.2%. Results. Including cases with manifest storage iron def iciency, a concordant elevated ZPP (>40 mu mol/mol haem) and a decreas ed transferrin saturation (<20%) were found in 23 of our dialysis pati ents (19.6%) while 55 cases (47%) were classified as concordantly nega tive. However, as many as 39 cases (33.3%) showed discrepant results: in 16 cases (13.6%) ZPP was elevated but transferrin saturation was in the normal range, while in 23 cases (19.6%) the opposite results were observed. Conclusions. We conclude that beyond the border of manifest storage iron deficiency, defined as a ferritin <30 ng/ml in male and (<15 ng/ml in female patients, ZPP and TS cover different ranges of fu nctional iron deficiency which is reflected in the lack of a correlati on of ZPP to any other of the above-mentioned parameters. Our data sug gest that a TS <20% as a diagnostic, and thus intervention, criterion in the evaluation of functional iron deficiency and iron substitution beyond manifest storage iron deficiency might result in overestimation of iron requirements. It remains to be shown in a longitudinal study, also reflecting the course of haemoglobin and the mean rHuEpo dose, w hether ZPP or TS is the more appropriate parameter in the evaluation o f functional iron availability.