The neurologic and psychiatric symptoms of VP and HCP are essentially identical to those found in AIP, and thus most information on porphyrias is usually discussed in relation to AIP, which only the specific testing information in additon. Rare ALA synthase deficiency porphyria is associated with elevated ALA . Often porphyria patients complain about the testing and retesting it takes to have a definitive diagnosis. It is also difficult to diagnosis an acute porphyria between attacks for a variety of reasons. The second reason is that abnormal concentrations of PBG typically normalize between attacks.
Enzyme concentrations can, in theory, identify individuals at risk.
For example, in individuals predisposed to acute intermittent porphyria, the enzyme PBG deaminase is typically half the levels seen in normal individuals. Many technical difficulties limit the practical usefulness of such enzyme assays, however, and gene-based assays will probably prove to be more reliable. Gene-based testing is currently available through Mt. Sinai for acute intermittent porphyria, but not for the other acute porphyrias. Cutaneous photosensitivity due to a porphyrin disorder is associated with elevated porphyrin concentrations. Bile and feces may also be used, although fecal porphyrins suffer from extensive bacterial degradation, and bile specimens are difficult to collect.