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Clin Chem. 2015 Dec;61(12):1453-6. doi: 10.1373/clinchem.2015.245456. Epub 2015 Oct 19.

Pitfalls in Erythrocyte Protoporphyrin Measurement for Diagnosis and Monitoring of Protoporphyrias.

Author information

1
University of Texas Medical Branch, Galveston, TX;
2
Icahn School of Medicine at Mt. Sinai, New York, NY;
3
University of California at San Francisco, San Francisco, CA;
4
University of Alabama at Birmingham, Birmingham, AL;
5
Wake Forest University, Winston-Salem, NC;
6
University of Utah, Salt Lake City, UT;
7
University of Washington, Seattle, WA.
8
University of Texas Medical Branch, Galveston, TX; kanderso@utmb.edu.

Abstract

BACKGROUND:

Laboratory diagnosis of erythropoietic protoporphyria (EPP) requires a marked increase in total erythrocyte protoporphyrin (300-5000 μg/dL erythrocytes, reference interval <80 μg/dL) and a predominance (85%-100%) of metal-free protoporphyrin [normal, mostly zinc protoporphyrin (reference intervals for the zinc protoporphyrin proportion have not been established)]; plasma porphyrins are not always increased. X-linked protoporphyria (XLP) causes a similar increase in total erythrocyte protoporphyrin with a lower fraction of metal-free protoporphyrin (50%-85% of the total).

CONTENT:

In studying more than 180 patients with EPP and XLP, the Porphyrias Consortium found that erythrocyte protoporphyrin concentrations for some patients were much higher (4.3- to 46.7-fold) than indicated by previous reports provided by these patients. The discrepant earlier reports, which sometimes caused the diagnosis to be missed initially, were from laboratories that measure protoporphyrin only by hematofluorometry, which is intended primarily to screen for lead poisoning. However, the instrument can calculate results on the basis of assumed hematocrits and reports results as "free" and "zinc" protoporphyrin (with different reference intervals), implying separate measurements of metal-free and zinc protoporphyrin. Such misleading reports impair diagnosis and monitoring of patients with protoporphyria.

SUMMARY:

We suggest that laboratories should prioritize testing for EPP and XLP, because accurate measurement of erythrocyte total and metal-free protoporphyrin is essential for diagnosis and monitoring of these conditions, but less important for other disorders. Terms and abbreviations used in reporting erythrocyte protoporphyrin results should be accurately defined.

PMID:
26482161
PMCID:
PMC4744648
DOI:
10.1373/clinchem.2015.245456
[Indexed for MEDLINE]
Free PMC Article

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