Effective control of patients with porphyria cutanea tarda by measuring plasma uroporphyrin

Abstract

The clinical value of a very rapid spectrofluorometric method for the determination of plasma uroporphyrin levels was studied during follow-up of 122 patients with porphyria cutanea tarda (PCT). Four-hundred and eight measurements were carried out within a 3-year period. In active PCT plasma uroporphyrin varied between 15 and 448 nmol/l (normal 0-1.4). A high correlation was seen between elevated levels of uroporphyrin in the plasma and urine in new cases (r = 0.72, n = 23) and relapses (r = 0.92, n = 37). A parallel course between these variables was noted during the treatment of 31 patients. The correlation was less pronounced (r = 0.42) in remission, i.e. in those cases with urinary uroporphyrin levels lower than 240 nmol/24 h. However, only in nine of 249 measurements taken in remission did plasma uroporphyrin exceed 15 nmol/l. In six of these cases a biochemical relapse had occurred at the next follow-up measurement as judged by an increase of uroporphyrin in the urine. It is suggested that treatment of new cases and relapses should continue until plasma uroporphyrin drops under 10 nmol/l. Values between 15 and 23 nmol/l in individuals already treated raise the suspicion of relapse and should be rechecked in the near future. Retreatment is necessary when the levels exceed 23 nmol/l. The use of the method is recommended as a simple and effective way for monitoring the progress of patients with PCT.