Fluorescence in red cells due to the presence of protoporphyrin appears in individuals with hereditary and acquired porphyrias; fluorescence due to zinc protoporphyrin is present in iron deficiency anemia and heavy metal (e.g., lead) poisoning. In general this is weak fluorescence around 590 nm, and should not be that well excited at 488 nm (the porphyrin absorption maximum is around 415 nm), but people looking specifically at samples from patients with porphyria, etc., have reported detecting it in instruments with 488 nm excitation. This probably doesn't have anything to do with the red cell autofluorescence discussed in recent postings on the Mailing List, but it's something to keep in mind. It may be feasible to make an inexpensive flow cytometer to measure this fluorescence using a violet diode laser. -Howard
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