Evaluation of a first-line spectrophotometric screening test for increased urine porphyrin excretion.

We compared a spectrophotometric screening test for urine porphyrin concentration with a high performance liquid chromatography (HPLC) method. The screening test gave lower values than those obtained by HPLC, but the overall correlation was good. Occasionally, spectrophotometry failed to detect porphyrins in the urine which were detected by HPLC. The type of porphyria had no influence on the efficacy of the screening method. Receiver operating characteristic plot analysis of the screening test led to a cut-off value of 110 nmol/24 h with a sensitivity of 96% and a specificity of 86%. We conclude that the spectrophotometric screening method is useful for detection of increased total urine porphyrin concentration.