Sorted By Test Name - Mayo Medical Laboratories

PTP
8731
Porphyrins, Total, Plasma
Clinical Information: The porphyrias are a group of inborn errors of metabolism resulting from
defects in the heme biosynthetic pathway. Enzymatic deficiencies result in the accumulation and excretion
of intermediary metabolites in different specimen types. The pattern of excretion of the heme precursors
in urine and feces and the accumulation within erythrocytes allow for the detection and differentiation of
the hereditary porphyrias. These accumulations cause characteristic clinical manifestations, which may
include neurologic and psychological symptoms and cutaneous photosensitivity, depending upon the
specific disorder. Although genetic in nature, environmental factors may exacerbate symptoms,
significantly impacting the severity and course of disease. Early diagnosis coupled with education and
counseling of the patient regarding the disease and treatment including avoidance of precipitating factors
are important for successful management. Historically, the porphyrias have been divided into 2 groups,
erythropoietic and hepatic based on the major site of substrate accumulation and/or overproduction.
Another classification is based on clinical presentation and divides the porphyrias into acute or nonacute
(cutaneous) categories. The acute porphyrias include acute intermittent porphyria (AIP), hereditary
coproporphyria (HCP), and variegate porphyria (VP). The nonacute porphyrias include congenital
erythropoietic porphyria (CEP), porphyria cutanea tarda (PCT), and erythropoietic protoporphyria (EPP).
PCT is the most common form of porphyria. It presents clinically with increased skin fragility and the
formation of vesicles and bullae on sun-exposed areas of the skin. PCT can be either sporadic (acquired)
or inherited in an autosomal dominant manner. A biochemical diagnosis of PCT is characterized by
increased urinary excretion of uroporphyrin and heptacarboxylporphyrin. Lesser amounts of
hexacarboxylporphyrin, pentacarboxylporphyrin, and coproporphyrin may also be excreted.
Hepatoerythropoietic porphyria (HEP) is observed when an individual inherits PCT from both parents.
Patients exhibit a similar porphyrin excretion pattern as PCT, although the clinical presentation is similar
to what is seen in CEP. The clinical features of the acute porphyrias include abdominal pain, sensory
neuropathy, and psychosis. Photosensitivity is not associated with acute intermittent porphyria (AIP), but
may be present in HCP and VP. The biochemical diagnosis of AIP is based upon an increased urinary
excretion of porphobilinogen (PBG) and aminolevulinic acid (ALA). In addition, uroporphyrin is also
usually increased. A urine specimen obtained during an acute episode is most informative, as these
analytes may be normal or only slightly increased between acute episodes of AIP. With respect to HCP
and VP, the excretion pattern observed in urine is indistinguishable from one another with elevations of
both coproporphyrin and PBG excretion being observed in urine. Fecal porphyrins analysis is
recommended to differentiate VP from HCP. CEP is a rare disorder typically presenting in childhood with
prominent photosensitivity and voiding of dark, wine-colored urine. A few milder adult-onset cases have
been documented as well as cases that are secondary to myeloid malignancies. A biochemical diagnosis of
CEP is characterized by increased urinary excretion of uroporphyrin and coproporphyrin with the
excretion of uroporphyrin usually exceeding that of coproporphyrin and the series I isomers
predominating. Lesser amounts of the heptacarboxyl-, hexacarboxyl-, and pentacarboxyl porphyrins may
be excreted. The urinary excretion of ALA and PBG is usually within normal limits. Typically, the work
up 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. Refer to The Challenges
of Testing For and Diagnosing Porphyrias, Mayo Medical Laboratories Communique 2002 Nov;27(11)
for more information.
Useful For: Differential diagnosis of porphyrias Differential diagnosis of photosensitive skin
manifestations Determining whether skin problems are related to an accumulation of porphyrins (renal
failure porphyria, porphyria cutanea tarda, congenital erythropoietic porphyria, and erythropoietic
protoporphyria) or some other problem
Interpretation: A mild elevation of total plasma porphyrins is an expression of a primary (eg, active
porphyria cutanea tarda, congenital erythropoietic porphyria, erythropoietic protoporphyria, variegate
porphyria, or hereditary coproporphyria) or secondary defect in the biosynthesis of heme. However, the
specific type of porphyria cannot be determined by total plasma porphyrin analysis alone. Porphyria
Biochemical abnormalities Acute intermittent porphyria Typically normal. May see increased
uroporphyrin. Congenital erythropoietic porphyria Increased uroporphyrin and coproporphyrin; if isomers
performed, series I isomers. Porphyria cutanea tarda Increased uroporphyrin and heptacarboxyl porphyrin
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