Test ID: PQNU
Porphyrins, Quantitative, Urine

Preferred screening test during symptomatic periods for acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria*

Preferred screening test to begin assessment for congenital erythropoietic porphyria and porphyria cutanea tarda*

*Additional confirmatory testing is required to make a diagnosis.

Preferred test during symptomatic periods for acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). Preferred test to begin assessment for congenital erythropoietic porphyria (CEP) and porphyria cutanea tarda (PCT).

Testing includes porphobilinogen.

A deficiency of any of the enzymes associated with the transformation of aminolevulinic acid (ALA) to heme can cause accumulations of porphyrinogens and porphyrins and the associated porphyria.

Persons with porphyria present with unusual and characteristic clinical manifestations. They have in common the excessive production and excretion of 1 or more of the porphyrins, porphyrinogens, and/or porphyrinogen precursors (ALA and porphobilinogen [PBG]).

Historically, the porphyrias have been divided into 2 groups, erythropoietic and hepatic based on the major site of expression of the enzyme defect. They may also be classified as acute or cutaneous based on the clinical symptoms.

A variety of toxins (eg, heavy metals, ethanol, halogenated aromatic chemicals, barbiturates) is known to interfere with heme synthesis and can cause porphyrinuria.

The pattern of excretion of the heme precursors in urine and feces and the accumulation within erythrocytes provide a major part of the basis for detecting and differentiating the hereditary porphyrias. The measurement of PBG in urine is important in evaluating for acute neurologic porphyrias including acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria. Urinary porphyrin determination is helpful in the diagnosis of these disorders, as well as other porphyrias including congenital erythropoietic porphyria and porphyria cutanea tarda. For additional information on the recommended order of testing, see Porphyria (Acute) Testing Algorithm and Porphyria (Cutaneous) Testing Algorithm in Special Instructions. Refer to The Challenges of Testing For and Diagnosing Porphyrias, Mayo Medical Laboratories Communique 2002 Nov;27(11) for more information regarding diagnostic strategy.

UROPORPHYRINS (octacarboxyl)

< or =30 nmol/24 hours

HEPTACARBOXYLPORPHYRINS

< or =9 nmol/24 hours

HEXACARBOXYLPORPHYRINS

< or =8 nmol/24 hours

PENTACARBOXYLPORPHYRINS

< or =10 nmol/24 hours

COPROPORPHYRINS (tetracarboxyl)

Males: < or =230 nmol/24 hours

Females: < or =168 nmol/24 hours

PORPHOBILINOGEN

< or =2.2 mcmol/24 hours

See The Heme Biosynthetic Pathway in Special Instructions.

In their acute phase, the acute porphyrias (acute intermittent porphyria [AIP], variegate porphyria [VP], and hereditary coproporphyria [HCP]) can be life threatening. Diagnosis depends on the measurement of increased urinary porphobilinogen (PBG) in the presence of the appropriate clinical symptoms. PBG elevation is often accompanied by increased urinary uroporphyrin with an increased ratio of uroporphyrin to heptacarboxyl-porphyrin. AIP can be confirmed by measurement of PBG deaminase activity (PBGD/88925 Porphobilinogen (PBG) Deaminase, Whole Blood). Enzyme measurement is also useful in family studies. VP and HCP can be confirmed by measurement of fecal porphyrins (FQPPS/81652 Porphyrins, Feces).

Diagnosis of porphyria cutanea tarda, which may or may not be familial, can be made when appropriate clinical symptoms are present and elevations of urinary uroporphyrin and heptacarboxylporphyrin are observed.

In congenital erythropoietic porphyria, urinary uroporphyrin and coproporphyrin are markedly elevated with a predominance of the series I isomers being excreted

Porphobilinogen (PBG) and porphyrins are susceptible to degradation at high temperature, at pH <7.0, and on exposure to light. Twenty-four hour urine collections should be preserved by adding 5.0 g of sodium carbonate to a light-resistant collection container prior to beginning collection.

Ethanol and a variety of medications are known to interfere with heme synthesis leading to elevations in urine porphyrins, particularly coproporphyrin. Coproporphyrin elevation without concomitant PBG elevation should not be used as the basis for the diagnosis of porphyria, but may warrant follow-up testing with fecal porphyrin analysis.

1. Tefferi A, Colgan JP, Solberg LA Jr: Acute porphyrias: diagnosis and management. Mayo Clin Proc 1994;69:991-995

2. Nuttall KL, Klee, GG: Tietz Textbook of Clinical Chemistry. 5th edition. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 2001, pp 584-607

3. Ellefson RD: Porphyrinogens, porphyrins and the porphyrias. Mayo Clin Proc 1982;57:454-458

• The Heme Biosynthetic Pathway
• Urine Preservatives
• Porphyria (Acute) Testing Algorithm
• Porphyria (Cutaneous) Testing Algorithm