Porphyrins faeces

Specimen:

A minimum of 2 g faeces; delivered to the laboratory within 5 h or frozen until delivered.

Method:

Spectrophotometry, fluorometry, HPLC.

Reference Interval:

Coproporphyrin:  < 30 µmol/kg dry weight

Protoporphyrin:  < 135 µmol/kg dry weight

Application:

Investigation of a patient with suspected porphyria. Faecal porphyrins are more likely to be abnormal in an asymptomatic patient than are urine porphyrins.

Interpretation:

Faecal porphyrin excretion is normal in acute intermittent porphyria but is increased in porphyria variegata and coproporphyria. Faecal porphyrins (isocoproporphyrin) are also increased in porphyria cutanea tarda. Separation of porphyrins is carried out by specialised laboratories and allows identification of characteristic patterns and markers for the differential diagnosis of porphyrias and for the investigation of porphyria in remission.

Reference:

Lecha M et al. Diagnosis and treatment of the hepatic porphyrias. Dermatol Ther. 2003;16(1):65-72. Review.