Erythropoietic protoporphyria. The problem of a suitable screening test.

Erythropoietic protoporphyria (EPP) is characterized by increased red cell protoporphyrins and is included in the differential diagnosis of children presenting with photosensitivity. In the past 20 years, using the traditional solvent extraction qualitative screening test for blood porphyrins, the diagnosis of EPP had been missed in 9 out of 10 patients but recently, using fluorescence microscopy of erythrocytes, no patients with EPP have been missed. All 14 patients in Northern Ireland known to have EPP were recalled and it was found that fluorescence microscopic determination was positive in all cases. We recommend fluorescence microscopy as the screening test of choice for the detection of increased red cell porphyrins.