Rapid diagnosis of iron deficiency by measurement of free erythrocyte porphyrins and hemoglobin: the FEP/hemoglobin ratio.

The concentration of free erythrocyte prophyrins (FEP) and of hemoglobin can be measured on blood samples spotted on filter paper. The FEP/hemoglobin ratio in iron deficiency increases exponentially with a decrease of both transferrin saturation and hemoglobin level. The FEP/hemoglobin is an indicator of imparied heme synthesis. In small children an elevation of the FEP/hemoglobin ratio is a better indicator of iron-deficiency anemia than low transferrin saturation. The FEP/hemoglobin ratio is normal in thalassemia trait and renal anemia but it may be elevated in sickle-cell anemia. Measurement of FEP and hemoglobin on filter paper provides a useful diagnostic tool for the diagnosis of iron deficiency, of anemia, and (in populations at risk) of leas intoxication.