How is a diagnosis of erythropoietic protoporphyria made?

Erythropoietic protoporphyria is believed to be due to a deficiency of the enzyme ferrochelatase. Red blood cells (RBCs) and feces show increased levels of protoporphyrins. In addition, if fresh RBCs are examined with a fluorescence microscope, 5% to 30% of RBCs will fluoresce a coral red color. This fluorescence is transient and light sensitive; thus, RBCs should be collected and examined in a dark room.

Murphy GM: Diagnosis and management of the erythropoietic porphyrias, Dermatol Ther 16:57–64, 2003.