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 abnormal, 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, and that most consistent with porphyria cutanea tarda (PCT), is an uro/hepta ratio < or =2.0 and an uro/iso ratio < or =18. When the uro/hepta or uro/iso ratios are less consistent with PCT, other less common porphyrin disorders should be considered. These include variegate porphyria, coproporphyria with manifestations of photosensitivity only, adult onset congenital porphyria, mixed porphyrias, and other less frequent porphyrin disorders. After initial evaluation, the diagnosis should ideally be confirmed by additional testing of blood and fecal specimens. Most attacks of the acute porphyrias are associated with a uro/hepta ratio >4, and can be confirmed by an elevated urine porphobilinogen concentration.