The Challenges Of Testing For And Diagnosing Porphyrias

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Why do you contact the ordering physician each time the coproporphyrin isomers test
(#8652 Coproporphyrin Isomers, Series I & III, Urine) is ordered?
The test for coproporphyrin isomers (#8652 Coproporphyrin Isomers, Series I & III, Urine) is often
ordered incorrectly. This assay is primarily utilized to rule in/out the hyperbilirubinemia disorders,
Dubin-Johnson or Rotor syndromes. It is not useful in the diagnosis of porphyrias. Bilirubin is derived
exclusively from heme metabolism. In Dubin-Johnson and Rotor syndromes, conjugated bilirubin accumulates
and transport is suppressed. Hyperbilirubinemia is the key feature of both syndromes. Patients with either
disorder have normal liver function tests and histologically normal livers with the exception of gross
pigmentation of the liver associated with Dubin-Johnson syndrome.
When the coproporphyrin isomers (#8652) test is ordered, referring physicians are contacted via telephone to
confirm the diagnosis in question as a means of ensuring the appropriate assay has been ordered. In most cases,
the physician is concerned about a potential porphyria diagnosis, and the 24-hour urine porphyrins test (#8562
Porphyrins, Quantitative, Urine) is the appropriate test to order. The specimen requirements are identical,
allowing for the coproporphyrin isomers to be canceled and the 24-hour urine porphyrins assay to be ordered.
This thereby reduces expenses billed in turn to the referring laboratory or physician, health insurance company,
and patient.
As a referring laboratory, you can aid in minimizing the turnaround time and telephone calls to you and your
referring physicians’ offices by confirming the suspected diagnosis prior to ordering testing or by providing
clinical information with the specimen. If you have questions regarding this, please contact a genetic counselor in
the Biochemical Genetics Laboratory by calling Mayo Laboratory Inquiry at 1-800-533-1710.
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What is the most appropriate MML test to order when I want an analysis of uroporphyrins and
coproporphyrins?
In most instances, testing for uroporphyrin and coproporphyrin is requested to rule out porphyria.
Urine porphyrin analysis (#8562 Porphyrins, Quantitative, Urine) provides quantitation of
uroporphyrins, coproporphyrins, the intermediate porphyrins (pentacarboxyl, hexacarboxyl, and
heptacarboxyl), and porphobilinogen. This test is generally the first step in evaluating a patient for porphyria.
The interpretive result provided will guide the clinician in selecting additional testing as necessary.
The analysis of coproporphyrin isomers (#8652 Coproporphyrin Isomers, Series I & III, Urine) is not a useful
diagnostic tool for the porphyrias. This test should not be utilized when testing of uroporphyrins and
coproporphyrins are desired.
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