[Red cell zinc protoporphyrin and its ratio to serum ferritin (ZPP/logSF index) in the detection of iron deficiency in patients with end-stage renal failure on hemodialysis].

Monitoring of iron metabolism has become a major clinical issue in end-stage renal patients undergoing hemodialysis. It can be done at three levels: storage, transport and marrow availability. The objective of that study was to evaluate if a combination of an iron storage marker, serum ferritin (SF) with red cell zinc protoporphyrin (ZPP), a marker of iron availability for erythron, will improve diagnostic value of both tests. In a baseline survey in the population of 186 haemodialysis patients (75% treated with rHuEpo), the following parameters were determined: complete blood count, serum transferrin saturation (TSAT), transferrin, SF, hypochromic red cells % (HRC) and ZPP; the ZPP/logSF ratio was calculated. Iron deficiency was defined as a fernitin saturation--TSAT < 20%. In the second part of the study, 24 pts with SF < 50 ng/ml were given 50 mg of i.v. iron weekly for three months, then the same tests were repeated. During that time the doses of rhuEpo were stable. An increase in hemoglobin of > 1.0 g/dl was considered as a positive response. In 186 studied patients mean SF was 274 +/- 335 ng/ml, and mean ZPP was 68 +/- 44 mumol/mol heme. A ZPP/logSF ratio > or = 40 had the best combination of diagnostic sensitivity and specificity in detecting iron deficiency (76% and 83% vs: 56% and 89% for ZPP > 90 mumol/mol heme, 84% and 34% for HRC > 5%, 68% and 58% for HRC > 10%) and the strong correlations with all other examined parameters were found. The index showed also the highest correlation with the response to the i.v. iron (r = 59; p < 0.01) of the tests evaluated. After three months the values of ZPP/logSF ratio decreased from 80 +/- 105 to 39 +/- 19 (p < 0.01). A significant difference between responders and nonresponders was found for basal ZPP/logSF (p < 0.05) but not for ZPP. Our data suggest that the ZPP/logSF index provides a new valuable parameter for the identification of hemodialysis patients with iron deficiency and the prediction an erythropoietic response to iron supplementation.