Zinc protoporphyrin, a useful parameter to address hyperferritinemia

Zinc protoporphyrin (ZPP) is produced instead of heme as soon as iron support to erythropoiesis becomes insufficient. In iron deficiency the intra-erythrocytic ZPP concentration is increased. The aim of this study was to investigate whether ZPP is influenced by increased iron levels in hereditary hemochromatosis (HE) and is useful in the clarification of hyperferritinemia. Twenty HE patients and 160 patients with hyperferritinemic caused by anemia of chronic disorders, liver diseases, transfusional iron overload and hematologic or solid malignancies were enrolled. ZPP was measured using the Aviv front-face hematofluorometer (normal <or= 40 micromol/mol heme). In HE, ZPP was significantly lower (median, 20 micromol/mol heme; p = 0.0005) compared to our historical control group. At diagnosis, 15 (75%) HE patients had ZPP values <or=25 micromol/mol heme. After phlebotomy, ZPP remained unchanged (median, 23 micromol/mol heme), although the initially high ferritin concentration decreased to normal. ZPP values in the other hyperferritinemic groups were significantly higher compared to HE and control groups. In contrast to HE, ZPP values <or=25 micromol/mol heme were only observed in 11% of cases with non-transfusional hyperferritinemia. The diagnostic accuracy of a ZPP <or=25 micromol/mol heme to detect HE in non-transfused hyperferritinemic patients was 87%, with a sensitivity of 75% and a specificity of 89%. Showing significantly lower values in HE, ZPP seems to be a useful parameter in distinguishing HE from other hyperferritinemic disorders as those conditions are generally accompanied by an increased ZPP.

Soluble transferrin receptor and zinc protoporphyrin--competitors or efficient partners?

OBJECTIVES

Soluble transferrin receptor (sTfR) and zinc protoporphyrin (ZPP) are both parameters of iron deficient erythropoiesis (IDE), the sTfR measurement is commonly regarded to be the more sensitive test. sTfR also reflects erythropoietic activity, it is increased in enhanced erythropoiesis.

METHODS

We investigated the diagnostic accuracy of sTfR in assessment of iron deficiency (ID) and compared it with ZPP. The study was performed on 174 subjects, in which ID has been precisely staged.

RESULTS

Individuals without ID and patients with storage iron depletion only, had normal sTfR values. Patients classified as IDE and patients with iron deficiency anemia had significantly increased sTfR. There was a good correlation between sTfR and hemoglobin (r = -0.86; P < 0.0001) and between sTfR and ZPP (r = 0.86; P < 0.0001). When diagnosing ID, ZPP was the more sensitive test. In mildly developed IDE associated with ZPP-ratios between 40 and 70 micromol/mol heme, the sTfR concentration was elevated in only 25% of the cases. Reliably elevated sTfR values were observed only in more advanced IDE, associated with ZPP > 70 mumol/mol heme.

CONCLUSIONS

ZPP is not inferior to sTfR when diagnosing IDE. Given the good correlation between sTfR and ZPP and because ZPP is uninfluenced by the erythropoietic activity, sTfR and ZPP are not competitors, rather efficient partners in diagnosing anemias. By measuring ZPP and sTfR simultaneously, the diagnostic uncertainty inherent in each of them individually can be eliminated. In particular, the simultaneous determination of ZPP and sTfR enhances the diagnostic power of sTfR in assessment of the erythropoietic activity.