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Common Test-Ordering Errors
Part 1: Misordered Tests

1,25-Dihydroxyvitamin D
PTH-related Peptide
Uroporphyrinogen III Synthase

Porphyria Enzymes

Slide 15

April 2010

The next misordered test I would like to discuss is red blood cell Uroporphyrinogen III Synthase—a test for 1 of the porphyrias. In our experience, Uroporphyrinogen III Synthase is mistakenly ordered on patients with possible acute intermittent porphyria. For which the correct test to order is red blood cell Porphobilinogen (PBG) Deaminase.

These 2 enzymes, uroporphyrinogen III synthase and porphobilinogen deaminase, are deficient in 2 very different porphyrias—1 is a very rare cutaneous porphyria that presents in infancy with blistering skin lesions (named congenital erythropoietic porphyria) and the other is an acute porphyria (called acute intermittent porphyria) that presents in the teen ages or older with abdominal pain, neuropathy, and psychiatric symptoms. With such different presentations, why are these 2 tests confused? Here I think the answer is pretty simple. An alternate name for porphobilinogen deaminase, the enzyme deficient in most cases of acute intermittent porphyria , is uroporphyrinogen I synthase). Hence, it may be that uroporphyrinogen I synthase (the enzyme affected in acute intermittent porphyria) gets confused with uroporphyrinogen III synthase, the enzyme deficient in congenital erythropoietic porphyria. Again, individuals placing orders must pay particular attention to the test name to avoid this error. And, because congenital erythropoietic porphyria diagnosed in infants, before sending in a specimen for congenital erythropoietic porphyria on an adult patient, it would be helpful to confirm the indication with the ordering physician. This is especially critical because acute intermittent porphyria can be a medical emergency and ordering the right test and getting the correct diagnosis in a timely fashion is very important.

Porphyria Enzymes


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