Abnormal chromatographic patterns of porphyrins in urine

Urine is the most frequent specimen used in the initial evaluation of adult patients who present with photosensitivity. When urine porphyrins are abno rmal, characterization of the chromatogram is facilitated by calculation of uroporphyrin-to-heptacarboxylate porphyrin (uro/hepta) and uroporphyrin-to -isocoproporphyrin (uro/iso) ratios. The most frequent abnormal pattern, an d that most consistent with porphyria cutanea tarda (PCT), is an uro/hepta ratio less than or equal to2.0 and an uro/iso ratio less than or equal to 1 8. When the uro/hepta or uro/iso ratios are less consistent with PCT, other less common porphyrin disorders should be considered. These include varieg ate porphyria, coproporphyria with manifestations of photosensitivity only, adult onset congenital porphyria, mixed porphyrias, and other less frequen t porphyrin disorders. After initial evaluation, the diagnosis should ideal ly be confirmed by additional testing of blood and fecal specimens. Most at tacks of the acute porphyrias are associated with a uro/hepta ratio >4, and can be confirmed by an elevated urine porphobilinogen concentration.