Porphyrins and Fluorescence
What's UP Doc? Is a regular column where we feature a patient question along with a response from a member of the UPA Scientific Advisory Board.
Does porphyrin in stool fluoresce under ultraviolet (UV) or Wood’s lamp?
Today’s answer comes from Dr. John Phillips of University of Utah School of Medicine in Salt Lake City.
The short answer is yes, porphyrin in stool will fluoresce under a Wood’s lamp (UV light).
Fluorescence is a phenomenon where a material will absorb a certain wavelength of light and then emit light at a different wavelength. In a dark room you can see the light being emitted.
Because of their molecular structure*, porphyrins fluoresce. They absorb light with a wavelength of about 400 nm (violet) and emit light in the 600nm range (orange/pink).
The fluorescent properties of porphyrins are used in some lab tests to differentiate between types of porphyria, because different porphyrins will emit slightly different wavelengths of light, which can be measured with a spectrophotometer. For example, plasma porphyrins in variegate porphyria (VP) emit light around 626nm compared to 615-620nm in porphyria cutanea tarda (PCT).
Porphyrins in samples of urine, stool and plasma fluoresce. However fluorescence on it’s own isn’t enough to diagnosis porphyria. Other measurement methods are used to determine the concentrations of porphyrins and porphyrin precursors and establish a porphyria diagnosis.
*NOTE: The term “porphyrin” refers to a type of molecule with a specific structure. ALA and PBG, which accumulate in the acute hepatic porphyrias (AIP, HCP and VP), are not porphyrins, and do not fluoresce.
Thank you to Dr. Phillips for this What's UP Doc? answer! Do you have a question for a porphyria expert? Send it to info@porphyria.org.
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