Sorted By Test Name - Mayo Medical Laboratories

PQNU
8562
HEXACARBOXYLPORPHYRINS
< or =2 nmol/L
PENTACARBOXYLPORPHYRINS
< or =5 nmol/L
COPROPORPHYRINS (tetracarboxyl)
< or =110 nmol/L
PORPHOBILINOGEN
< or =1.3 mcmol/L
See The Heme Biosynthetic Pathway in Special Instructions.
Clinical References: 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 Textbook 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 Metabolic Basis of Inherited Disease. Eighth edition. Edited by CR
Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill BookCompany, 2001, pp 2991-3062
Porphyrins, Quantitative, Urine
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. Urinary porphyrin determination is helpful in the diagnosis of
most porphyrias including congenital erythropoietic porphyria (CEP), porphyria cutanea tarda (PCT),
acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). In
addition, measurement of porphobilinogen (PBG) in urine is important in establishing the diagnosis of the
acute neurologic porphyrias (AIP, HCP, and VP). Neither urine porphyrins nor PBG are helpful in
evaluating patients suspected of having erythropoietic protoporphyria (EPP). 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 AIP, HCP, and
VP. The nonacute porphyrias include CEP, PCT, and 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 AIP, but may be present in HCP and VP. The biochemical diagnosis of AIP is based upon an
increased urinary excretion of 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
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