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The porphyrias are a group of inherited disorders resulting from enzyme defects in the heme biosynthetic pathway. Depending on the specific enzyme involved, various porphyrins and their precursors accumulate in different specimen types. The patterns of porphyrin accumulation in erythrocytes and plasma and excretion of the heme precursors in urine and feces allow for the detection and differentiation of the porphyrias.
Testing protoporphyrin fractions is most informative for patients with a clinical suspicion of erythropoietic protoporphyria (EPP) or X-linked dominant protoporphyria (XLDPP). Clinical presentation of EPP and XLDPP is identical with onset of symptoms typically occurring in childhood. Cutaneous photosensitivity in sun-exposed areas of the skin generally worsens in the spring and summer months. Common symptoms may include itching, edema, erythema, stinging or burning sensations, and occasionally scarring of the skin in sun-exposed areas. Although genetic in nature, environmental factors exacerbate symptoms, significantly impacting the severity and course of disease.
EPP is caused by diminished ferrochelatase activity resulting in significantly increased free protoporphyrin levels in erythrocytes, plasma, and feces.
X-linked dominant protoporphyria is caused by gain-of-function mutations in the C-terminal end of ALAS2 gene and results in elevated erythrocyte levels of free and zinc-complexed protoporphyrin, and total protoporphyrin in plasma and feces.
Other possible cases of elevated erythrocyte zinc-complexed protoporphyrin may include:
-Iron-deficiency anemia, the most common cause
-Chronic intoxication by heavy metals (primarily lead) or various organic chemicals
-Congenital erythropoietic porphyria (CEP), a rare autosomal recessive porphyria caused by deficient uroporphyrinogen III synthase
-Hepatoerythropoietic porphyria (HEP), a rare autosomal recessive porphyria caused by deficient uroporphyrinogen decarboxylase
Typically, the workup of patients with a suspected porphyria is most effective when following a stepwise approach. See Porphyria (Acute) Testing Algorithm and Porphyria (Cutaneous) Testing Algorithm in Special Instructions or contact Mayo Medical Laboratories to discuss testing strategies.
There are 2 test options: PPFE / Protoporphyrins, Fractionation, Whole Blood and PPFWE / Protoporphyrins, Fractionation, Washed Erythrocytes. The whole blood option is easiest for clients but requires that the specimen arrive at Mayo Medical Laboratories within 7 days of draw. When this cannot be ensured, washed frozen erythrocytes, which are stable for 14 days, should be submitted.
Preferred test for analysis of erythrocyte protoporphyrin fractions
Preferred test for evaluating patients with possible diagnoses of erythropoietic protoporphyria and X-linked dominant protoporphyria
Establishing a biochemical diagnosis of erythropoietic protoporphyria, and X-linked dominant protoporphyria
Abnormal results are reported with a detailed interpretation that may include an overview of the results and their significance, a correlation to available clinical information provided with the specimen, differential diagnosis, and recommendations for additional testing when indicated and available.
Patients must abstain from alcohol for at least 24 hours. Alcohol suppresses enzyme activity potentially leading to false-positive results.
The preferred test for lead toxicity in children is blood lead (see PBBD / Lead with Demographics, Blood).
<20 mcg/dL packed cells
<60 mcg/dL packed cells
1. Tortorelli S, Kloke K, Raymond K: Chapter 15: Disorders of porphyrin metabolism. In Biochemical and Molecular Basis of Pediatric Disease. Fourth edition. Edited by DJ Dietzen, MJ Bennett, ECC Wong. AACC Press 2010, pp 307-324
2. Nuttall KL, Klee GG: Analytes of hemoglobin metabolism-porphyrins, iron, and bilirubin. In Tietz Fundamentals of Clinical Chemistry. Fifth edition. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 2001, pp 584-607
3. Anderson KE, Sassa S, Bishop DF, Desnick RJ: Disorders of Heme Biosynthesis: X-Linked Sideroblastic Anemia and the Porphyrias In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by Valle D, Beaudet AL, Vogelstein B, et al. New York, McGraw-Hill, 2014. Accessed June 27, 2016. Available at http://ommbid.mhmedical.com/content.aspx?bookid=971&Sectionid=62638866
4. Whatley SD, Ducamp S, Gouya L, et al: C-terminal in the ALAS2 gene lead to gain of function and cause X-linked dominant protoporphyria without anemia or iron overload. Am J Hum Genet 2008 Sep;83(3):408-414