Composition of urinary coproporphyrin isomers I-IV in human porphyrias

The urinary distribution and relative proportions of the four coproporphyrin isomers I-IV were investigated in 50 patients suffering from hepatic and erythropoietic types of hereditary porphyrias. A highly efficient sample preparation method was applied to isolate urinary coproporphyrins, the isomer ratios of which were quantitated by isocratic ion-pair high-performance liquid chromatography. Results showed a significant decrease (p < 0.001) of the proportion of coproporphyrin I in acute hepatic porphyria (acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, porphobilinogen synthase deficiency porphyria) as compared with chronic hepatic porphyria (porphyria cutanea tarda, chronic hepatic porphyria type B and C) (13.2 +/- 5.3%, mean +/- S.D., vs. 31.4 +/- 11.5%). Conversely, the proportion of isomer III was significantly higher (p < 0.001) in acute hepatic porphyria than in chronic hepatic porphyria (80.9 +/- 5.2% vs. 62.2 +/- 10.9%). As expected, the highest level of coproporphyrin I (90.0 +/- 1.9%) was found in congenital erythropoietic porphyria. The atypical coproporphyrins II and IV were detected in all types of porphyria analysed and ranged from 0.2 to 9.0%; no significant differences were seen between acute and chronic hepatic porphyrias. The diagnostic importance of the isomer ratios of coproporphyrins I and III has been confirmed in our study, while the significance of the atypical coproporphyrin isomers II and IV is still unclear at present.