Erythropoietic protoporphyria: a quantitative determination of erythrocyte protoporphyrin in individual cells by flow cytometry.

A fraction of the erythrocytes from patients with erythropoietic protoporphyria contains large amounts of protoporphyrin. By extraction methods, only a mean value of the protoporphyrin content in erythrocytes is obtained. In this study, flow cytometry was used to determine the protoporphyrin content in each individual erythrocyte. The mean erythrocyte protoporphyrin fluorescence, calculated from flow cytometric data, correlated linearly to the mean cellular protoporphyrin concentration measured by ethyl acetate/acetic acid extraction. This indicates that flow cytometry gives a reliable quantitative determination of protoporphyrin in individual cells. Erythrocytes from patients with erythropoietic protoporphyria had a markedly skewed distribution of protoporphyrin. In the most fluorescent erythrocytes (protoporphyrin concentration 3.3 mM), there was about one protoporphyrin molecule for every sixth haeme molecule. This might explain the slight anaemia in some of these patients.