A rapid assay for urinary porphyrins by dual-wavelength spectrophotometry

A procedure has been developed for the separation and quantitative assay of urinary porphyrins. Urine was directly diluted to a final concentration of 1 MHCl and the amount of porphyrins was determined from the peak-to-trough height deflection of the first derivatives of the absorption spectrum in the region of the Soret band. The ratio uro-/coproporphyrin was determined from the wavelength at which the spectrum intercepted the baseline. The specificity (as shown by a correlation coefficient of 0.99 compared to the method of Doss and Schmidt (1971) Z. Klin. Chem. Klin. Biochem. 9, 415-418), precision (coefficient of variation 5.2 percent) and sensitivity (lower detection limit approx. 0.01 mumol/l) of the present method were highly sufficient to estimate total and different porphyrins in the routine laboratory.