Testing

About lab tests

Misinterpretation of porphyria test results
Diagnosis of porphyria is often delayed, and it has become widely recognized that physicians should maintain a high index of suspicion for these conditions. It is less widely appreciated that incorrect diagnoses of porphyria are common in patients with symptoms due to other diseases. Therefore, in patients with a past history of porphyria, it is important to review the laboratory data that were the basis for the original diagnosis. Further testing may be necessary if the diagnosis was not adequately documented.

Incorrect diagnoses of porphyria can occur in patients having minimal abnormalities in laboratory tests, such as small elevations in urinary porphyrins or porphyrin precursors that in fact have little or no diagnostic significance. Incorrect diagnoses are less likely if reliance is placed on a few first-line tests in most clinical situations, as described above. Overuse and over interpretation of minor abnormalities in results of second-line tests including erythrocyte PBGD, other enzyme assays, and fractionation of urinary and fecal porphyrins, account for many incorrect diagnoses of porphyria.