IDENTIFICATION OF ACUTE PORPHYRIA - EVALUATION OF A COMMERCIAL SCREENING-TEST FOR URINARY PORPHOBILINOGEN

A commercial semi-quantitative kit (Trace) for urinary porphobilinogen (PBG) in which urine is pre-treated with ion-exchange resin and the c olour of the Ehrlich-PBG adduct matched against a set of surrogate sta ndards was compared with qualitative screening methods (Watson-Schwart z) in common use. Twenty samples in which PEG had been quantitated wer e blindly tested by both methods in each of 13 typical user laboratori es. For urine samples with raised PEG: 123 out of 129 results were pos itive when tested with the Trace kit. Using qualitative tests routinel y in use in the various laboratories only 45 out of 119 results were u nequivocally positive. Sixteen out of 91 results for pigmented urine s amples with normal PEG were reported as positive using qualitative scr eening tests, but only one using the Trace kit. Therefore, the Trace m ethod is far more sensitive and specific than the qualitative screenin g tests. It is recommended that Watson-Schwartz-type screening tests s hould be abandoned and, ideally, all urine samples analysed by quantit ative methods. However, the Trace method is a convenient alternative w hich is adequate for the initial screening of symptomatic patients.