REFERENCE INTERVALS FOR 24-HOUR AND RANDOM URINE PORPHYRINS

Urine porphyrin analysis is an important part in evaluation of photose nsitivity. Since porphyrin excretion is variable throughout the day, a nalysis is traditionally based on 24-hour collections. To facilitate t he use of random specimens, as well as poorly collected 24-hour specim ens, reference limits based on the porphyrin to creatinine ratio have been developed. Based on 1,171 adult specimens, it is estimated that t he 95 percent reference limit (90 percent confidence interval) is less than or equal to 3.9 (3.5-5.7) mu mol/mol of creatinine for uroporphy rin and less than or equal to 22 (19-34) mu mol/mol for coproporphyrin . These values apply to both 24-hour and random specimens, although ra ndom specimens show a higher degree of variability. Modest differences exist between males and females, but they are not significant given t he degree of uncertainty in the confidence intervals. In terms of more traditional 24-hour units, reference limits correspond to less than o r equal to 37 (32-63) nmol/day for uroporphyrin and less than or equal to 221 (195-320) nmol/day for coproporphyrin.