A sensitive method of screening for urinary porphobilinogen

In this screening method for urinary porphobilinogen (PBG), urine is added to Dowex 2 resin under alkaline conditions in a test tube and mixed. The supernate is removed and the adsorbed PBG is eluted with acid and reacted with Ehrlich's reagent. We compared results with those by the Watson-Schwartz screening method, using urine samples from normal people with and without added PBG. At a PBG concentration of about five times the upper limit of normal, the resin method gave a sensitivity of 100%; the Watson-Schwartz method gave a sensitivity of 51%. At lower PBG concentrations of just over and twice the upper limit of normal, the sensitivity by the resin method was respectively 97% and 100%. With normal urine samples, the resin method gave negative results for all samples (100% specificity) and the Watson-Schwartz had 95% specificity. Our data indicate that the resin method is sensitive, specific, and reliable and is superior to the Watson-Schwartz method.