Dialysis Transplantation Experience with zinc protoporphyrin as a marker of endogenous iron availability in chronic haemodialvsis patients

Background. Ferritin and the percentage of transferrin saturation (TS) are established parameters with which to evaluate endogenous iron availability during treatment of renal anaemia with recombinant human erythropoietin (rHuEpo). Zinc protoporphyrin (ZPP) has been proposed as another valid marker in this setting. Methods. We determined the following parameters in 127 patients, including 117 haemodialysis patients: haemoglobin, erythrocytes, haematocrit, mean corpuscular volume (MCV), iron, ferritin, transferrin saturation and ZPP. Of the patients treated in a crosssectional study, 38.5% were treated with rHuEpo; 30.7% with intravenous iron; and 13.6% with intravenous iron and rHuEpo simultaneously. Median ferritin was 304 ng/ml and median transferrin saturation was 21.2%. Results. Including cases with manifest storage iron deficiency, a concordant elevated ZPP (>40 umol/mol haem) and a decreased transferrin saturation (<20%) were found in 23 of our dialysis patients (19.6%) while 55 cases (47%) were classified as concordantly negative. 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 functional iron deficiency which is reflected in the lack of a correlation of ZPP to any other of the above-mentioned parameters. Our data suggest 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 Correspondence and offprint requests to: Dr M. Baldus, Medizinische KJinik A, Bremserstr. 79, Klinikum der Stadt 67063, Ludwigshafen am Rhein, Germany. rHuEpo dose, whether ZPP or TS is the more appropriate parameter in the evaluation of functional iron availability.