Yeast, creatinine and false diagnosis of porphyria.

A distressingly common occurrence is the erroneous diagnosis of hepatic porphyria in patients with chronic abdominal pain in which either urinary porphyrins are elevated and/or Watson-Schwarz test is positive. This work investigates a characteristic case and points at possible pitfalls in establishing a diagnosis. In the patient described, spot urine analysis showed positive Watson-Schwarz test and increased porphyrins at three separate occasions, while normal values of precursors and porphyrins were recorded in 24-hrs. urinary collections during four hospitalization periods for acute abdominal pain. Various colorimetric and HPLC methods employed excluded the diagnosis of porphyria and led to resolving the discrepancy between home and hospital results. It was found that the false increase in porphyrins in the spot samples emerged from a substance present in yeast tablets which the patient was consuming. The positive Watson-Schwarz test obtained was probably the result of the fact that the urine samples were concentrated with creatinine values exceeding 400 mg%. The case reported above, as well as studies carried out in three healthy volunteers and in an AIP patient, led to the conclusion that in order to obtain reliable result, 24-hrs. urinary collections should be examined, rather than spot urine samples.