The Biochemical Diagnosis of the Porphyrias

The aim of diagnosis is the characterization of a patient's disease so that the optimal therapy may be instituted. The precision of the diagnosis depends on the knowledge available and the sensitivity of the techniques used to exploit that knowledge, and major methodological advances in recent years have provided the scientific investigator with an extensive array of sophisticated techniques. The choice of which test is best for the diagnosis of a particular disease is particularly difficult when dealing with the disorders of porphyrin metabolism as simple, cheap tests are available to identify a patient as “porphyric.” This diagnosis is not sufficient, however, as the term “porphyria” encompasses a number of different disorders, each a manifestation of deficient enzyme activity at different stages in the heme biosynthetic pathway. While all are characterized by excessive production, accumulation, and excretion of porphyrins and porphyrin precursors, the pattern thereof is specific for each particular type of porphyria and each is a discrete clinical entity demanding a different therapeutic approach. It thus cannot be over emphasized that the porphyric patient's disease must be meticulously defined and when simple tests are insufficient for this, sophisticated techniques should be employed, preferably in laboratories committed to porphyrin study. Before discussing the best way to make a diagnosis, however, it is clearly important to define the terms used.