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Unit Code 80313:
Xanthine and Hypoxanthine, Urine

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Useful For

Diagnosis and confirmation of xanthinuria

 

Evaluation of low serum or urine uric acids

 

Evaluation of allopurinol treatment in hyperuricemic disorders

(e.g., Lesch-Nyhan syndrome)

Clinical Information

Xanthine and hypoxanthine are the precursors of uric acid, the end

product of purine metabolism. Two inborn errors of metabolism are

characterized by elevated excretion of xanthine and hypoxanthine.

 

Isolated xanthine dehydrogenase (XDH, xanthine oxidase) deficiency:

Patients with isolated XDH deficiency may remain asymptomatic, but

nephrolithiasis due to the insolubility of xanthine, may occur at any age.

Some patients also develop a myopathy with crystalline xanthine deposits

in muscle.

 

Combined deficiency of SDH and the related enzyme sulfite oxidase (SO):

Combined XDH/SO deficiency is also characterized by nephrolithiasis,

but more prominently by the symptoms of SO deficiency (isolated SO

deficiency also occurs) which include neonatal seizures, myoclonus,

lens dislocation, and severe mental retardation. This form of xanthinuria

is caused by molybdenum cofactor deficiency, which is required for

the activity of both oxidases.

 

Elevations of xanthine and hypoxanthine and abnormally low levels

of uric acid are found in both disorders, while in patients with XDH/SO

deficiency sulfites and sulfur-containing metabolites (S-sulfocysteine,

thiosulfate, taurine) also accumulate.

 

Allopurinol, a xanthine oxidase inhibitor that prevents conversion of

xanthine to uric acid, is used to treat hyperuricemia.

Reference Values

HYPOXANTHINE: 

20-100 umol/24 hours

XANTHINE: 

20-60 umol/24 hours

Interpretation

Abnormal concentrations of xanthine and hypoxanthine will be reported

along with an interpretation. The interpretation of an abnormal metabolite

pattern will include an overview of the results and of their significance, a

correlation to available clinical information, possible differential diagnoses,

recommendations for additional biochemical testing and confirmatory studies

(enzyme assay, molecular analysis), name and phone number of contacts

who may provide these studies at the Mayo Clinic or elsewhere, and a number

for one of the laboratory directors if the referring physician has additional

questions.  Increased urinary xanthine and hypoxanthine with low urinary uric

acid are characteristic of xanthine oxidase deficiency.

 

Increased urinary excretion of xanthine, hypoxanthine, and uric acid are

indicative of hyperuricemia disorders treated with allopurinol.

Cautions

No significant cautionary statements

Special Instructions and Forms

• Urine Preservatives 

Clinical Reference

Raivio KO, Saksela M, Lapatto R:  Xanthine oxidoreductases -

Role in human pathophysiology and in hereditary xanthinuria.  

 In The Metabolic and Molecular Bases of Inherited Disease.  

8th edition.  Edited by CR Scriver, AL Beaudet, WS Sly, et al.  New York,

McGraw-Hill Book Company, 2001, pp 2639-2652

 

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