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Clinical Information: The porphyrias are a group of inherited disorders resulting from an enzyme
deficiency in the heme biosynthetic pathway. Depending on which enzyme is deficient, various
porphyrins and their precursors accumulate in plasma, erythrocytes, and tissues, and are excreted in the
urine, feces, or both. The porphyrias can be classified as either erythropoietic or hepatic. Both the
erythropoietic porphyrias and the chronic hepatic porphyrias are associated with cutaneous
photosensitivity, but not with the neurological symptoms that accompany the acute hepatic porphyrias.
Diagnosis of the erythropoietic porphyrias (ie, erythropoietic protoporphyria [EPP] and congenital
erythropoietic porphyria [CEP]) can be determined by analysis of porphyrins in the erythrocytes.
Erythrocyte (RBC) porphyrins consist almost entirely of protoporphyrin. Increased RBC protoporphyrin
is characteristic of EPP and of the intoxication porphyrias that may be caused by heavy metals,
halogenated solvents, some pesticides, and medications. However, iron deficiency anemia is the most
common cause of increased RBC protoporphyrin. Therefore, when total RBC porphyrins are elevated,
fractionation and quantitation of zinc-complexed and noncomplexed (free) protoporphyrin are necessary
to differentiate the inherited porphyrias from other causes of elevated porphyrin levels. Zinc-complexed
protoporphyrin may be increased in RBCs in association with: -Iron-deficiency anemia (the most common
cause of elevated zinc protoporphyrin) -Chronic intoxication by heavy metals (primarily lead) or various
organic chemicals -CEP -Hepatoerythropoietic porphyria, a rare form of porphyria caused by homozygous
or compound heterozygous mutations in the uroporphyrinogen decarboxylase gene (UROD) -X-linked
dominant protoporphyria, a form of protoporphyria caused by a gain of function mutation in the
C-terminal end of ALAS2 gene Free protoporphyrin is increased in RBCs in association with EPP, an
erythropoietic porphyria that is inherited in an autosomal dominant fashion. EPP is considered to be the
third most common form of porphyria. It is caused by diminished ferrochelatase activity, which results in
increased free protoporphyrin levels in RBCs, plasma, and feces. Onset of symptoms typically occurs in
childhood with cutaneous photosensitivity in sun-exposed areas of the skin, generally becoming worse 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. CEP is an erythropoietic
porphyria that is inherited in an autosomal recessive fashion. CEP is caused by uroporphyrinogen III
synthase deficiency, which results in the accumulation and excretion of uroporphyrin I and
coproporphyrin I in urine and feces. Circulating RBCs contain measurable amounts of uroporphyrin and
coproporphyrin. RBC zinc protoporphyrin may also be elevated due to increased erythropoiesis.
Symptoms typically present in early infancy with red-brown staining of diapers, severe cutaneous
photosensitivity with fluid-filled bullae and vesicles. Other common symptoms may include thickening of
the skin, hypo- and hyperpigmentation, hypertrichosis, cutaneous scarring, and deformities of the fingers,
eyelids, lips, nose, and ears.
Useful For: Diagnosis of erythropoietic protoporphyria and congenital erythropoietic porphyria
Evaluation of chronic intoxication from exposure to a variety of agents including heavy metals and
chemicals Differentiating iron-deficiency anemia from other causes of elevated porphyrin levels There are
2 test options: PEE/88886 Porphyrins Evaluation, Whole Blood and PEWE/31893 Porphyrins Evaluation,
Washed Erythrocytes. The whole blood option is easiest for clients but requires that the specimen arrive at
Mayo Medical Laboratories within 48 hours of draw. When this cannot be ensured, washed RBCs should
be submitted.
Interpretation: An elevation of total RBC porphyrins can be an expression of a primary or secondary
defect in the biosynthesis of heme. However, the specific type of porphyria cannot be determined by total
porphyrin analysis alone. Total RBC porphyrin values >80 mcg/dL suggest the existence of an
intoxication problem or a metabolic problem that involves accelerated erythropoiesis. If the total RBC
porphyrin concentration is elevated, additional testing (fractionation assays) is required to identify and
quantify the specific affected porphyrin. Increased total RBC porphyrin concentrations may be due to:
-Free protoporphyrin, the predominant form that is elevated in patients with erythropoietic protoporphyria
-Zinc protoporphyrin, elevated in patients with heavy metal intoxication or iron deficiency anemia
-Uroporphyrin and coproporphyrin, preferentially elevated in patients with congenital erythropoietic
porphyria A written interpretation is included with all reports. When abnormal results are detected, a
detailed interpretation is given, including: -An overview of the results and their significance -Elements of
a differential diagnosis -Recommendations for additional biochemical testing A normal RBC porphyrin
evaluation does not rule out other forms of porphyria including porphyria cutanea tarda (PCT), acute
intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). See The
Heme Biosynthetic Pathway in Special Instructions.
Current as of January 3, 2013 2:22 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1454