Rates of plasma porphyrin disappearance in fluorescent vs. red incandescent light exposure.

The rates of porphyrin disappearance in plasma specimens were assessed during exposure to standard fluorescent room lighting. Protoporphyrin half-life in specimens from patients with erythropoietic protoporphyria appeared to be less than 30 min under these conditions. Uroporphyrin-coproporphyrin mixtures in plasmas of patients with porphyria cutanea tarda were more photostable, with half-lives measurable in terms of hours. All plasma porphyrins could be protected for several days from similar photodegradation by performing all blood drawing, processing, and assay procedures under ordinary red-incandescent illumination, and by storage in the dark.