Description
Porphyrins are precursors of heme, which is a cofactor in hemoglobin, myoglobin and the cytochromes.
Porphyrins play an important role in the oxygen metabolism. Heme biosynthetic activity is located quantitatively in bone marrow and liver. There are several genetic defects of heme biosynthesis described, and all of them show an increase of porphyrins. The laboratory diagnosis and classification of porphyrin disorders are based primarily on the measurement of the excretion of porphyrins and porphyrin precursors, mainly in urine. Uro-, copro-, penta- and tri carboxy porphyrin, are increased in autosomal dominant acute porphyrin disorders. In chronic porphyrin disorders, including porphyria cutanea tarda, uro- and hepta- porphyrin are elevated. In chronic lead intoxication, the coproporphyrins are slightly increased (0.5–2µmol/24h urine), and acute lead poisoning is characterized by extremely high excretion of total porphyrins (up to 15µmol/24h urine).
