Usefulness of erythrocyte protoporphyrin test in the puerperium compared to the soluble transferrin receptor

Erythrocyte protoporphyrin (EP), serum ferritin (SF), soluble transferrin receptor (sTfR) and routine hematological laboratory tests were studied in 77 women 24 h post-partum, assisted at Paroissien Hospital (in Buenos Aires Province). Hematocrite (Hct), hemoglobin (Hb), red blood cells (RBC) and white blood cells (WBC) were determined using an electronic counter (Mega); EP by Piomelli's; SF by ELISA (IMx Ferritina, Abbott); sTfR by ELISA (Orion Diagnostica) and C-Reactive Protein (PCR-Latex, Wiener lab). All determinations were made in fasting blood samples. Statistical analysis (Receiver Operating Characteristics, ROC) were performed using Med Calc software. The soluble transferrin receptor (sTfR) was used as gold standard. (mean +/- SD): Hct (%) 35 +/- 5; Hb (g/l) 113 +/- 18; RBC x 103/mm3 3,893 +/- 489; MCV (fL) 90 +/- 6; WBC/mm3 9,543 +/- 2,669; EP (microg/dl RBC) 46 +/- 39; sTfR (mg/l) 4.7 +/- 2.8; SF (microg/l) 26 +/- 31; PCR (Pos/Neg) 72/5. EP did not correlate with SF but it did with sTfR (r=0.323, p=0.007). Sensitivity (Se) and specificity (Sp) of SF and EP were, respectively: 83% and 63% for a cut-off point of 25 microg SF/L; 38% and 90% for a cut-off point of 53 microg EPdl RBC. These results suggest that EP might be a useful and cheap indicator to assess maternal Fe nutritional status during the early perinatal period in hospital laboratories, allowing the detection of 16% of women presenting normal Hb values.