Performance of screening tests for porphyria.

The clinical utility of screening tests for porphyria has been assessed in 201 cases referred to Northwick Park Hospital. Routine screening in the referring laboratories was unreliable giving both false negative and positive results. Only 43% of porphyrics were correctly identified, apparently due to poor analytical sensitivity. Evidence is presented to show that the adoption of alternative semiquantitative tests for porphyrins employing spectrophotometric scanning of acidified urine or of faecal extracts will overcome many of these problems.