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Unit Code 8599:
Uroporphyrinogen Decarboxylase (UPG D), Erythrocytes

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Useful For

Diagnosis of PCT and HEP

Clinical Information

Porphyria cutanea tarda (PCT), the most prevalent form of porphyria,

and the rare hepatoerythropoietic porphyria (HEP) -- are caused by

deficiency of Upg D activity with accumulation of uroporphyrins and

hepta-, hexa-, and pentacarboxyl porphyrins in skin, subcutaneous

tissues, and liver.

 

In both PCT and HEP, photosensitivity with vesicular and bullous

lesions on exposed surfaces of hands, arms, face, and legs, and

fragility of the skin in relation to physical trauma. Other characteristics

may include hypertrichosis, hyperpigmentation, and hyperkeratosis.

The problems of PCT present mainly in adulthood; however, rare

cases of PCT have been reported in childhood. HEP presents in

early childhood.

Reference Values

1.0-3.0 Relative Units (normal)

0.80-0.99 Relative Units (marginal)

<0.80 Relative Units (porphyria cutanea tarda or

hepatoerythropoietic porphyria)

See "Porphyrinogens, Porphyrins, and Porphyrias"

in Special Instructions.

Interpretation

Upg D activity <0.80 Relative Units indicates PCT or HEP.

 

Increased urinary excretion of uroporphyrins and hepta-, hexa-, and

pentacarboxyl porphyrins occurs in both inheritable PCT and "acquired

PCT" -- which is a form of intoxication porphyria -- and in HEP.  In most

cases of inheritable PCT and in HEP, the erythrocyte Upg D activities

will be diminished. Therefore, increased urinary uroporphyrins and

hepta- , hexa-, and pentacarboxyl porphyrins and diminished activity of

erythrocyte Upg D provide a definitive basis for a biochemical diagnosis

of either PCT or HEP.

 

With entirely normal levels of erythrocyte Upg D, as in "acquired

PCT" and in some cases of inheritable PCT, increased excretion of

uroporphyrins and of hepta-, hexa-, and pentacarboxyl porphyrins will

be found. This is attributed to a probable defect in the Upg D activities of

nonerythroid cells, and particularly of hepatocytes.

Cautions

Abstinence from alcohol is essential for at least 24 hours.

 

It is essential to proceed expeditiously with obtaining, processing,

and dispatching the specimen, following PRECISELY procedures

specified in the "Specimen Requirements" and paying special

heed to maintaining low temperatures. Failure to do so will allow

enzyme damage, resulting in falsely low values (ie, false-positive).

Special Instructions and Forms

• Porphyrinogens, Porphyrins, and Porphyrias 
• Porphyria (Acute) Testing Algorithm 
• Porphyria (Cutaneous) Testing Algorithm 

Clinical Reference

Ellefson RD: Porphyrinogens, porphyrins, and the porphyrias. Mayo

Clin Proc 1982;57:454-458

Key