Urate (Blood)

Diagnostic Use

Uric acid is increased in gout, renal failure, polycythaemia, and a number of neoplastic disorders where there is a significantly increased cell turnover (e.g. leukaemia, myeloma, lymphoma).

Hyperuricemia in Gout

• In asymptomatic hyperuricaemia, the 5 year cumulative incidence of first gout attack increases with increasing serum urate: from around 0.6% (at serum urate <0.42 mmol/L) to more than 20% (at serum urate >0.59 mmol/L). However, hypouricaemic therapy may not be indicated in asymptomatic hyperuricaemia unless urate level is very high.
• The incidence of recurrent gouty arthritis at serum urate of 0.42mmol/L is about twice as high compared with serum urate of 0.36mmol/L after 1 year of follow up.
• Serum urate level often falls during acute attack of gouty arthritis, so a normal serum urate during acute attack does NOT exclude the diagnosis of gout.
• A raised serum urate level is not sufficient to make the diagnosis of gout, which requires:
  a. Classical history of podagra
  b. Identification of urate crystals in joint fluid, or
  c. (In late cases), typical x-ray changes.

Hypouricaemic therapy:
For optimal control of gouty arthritis, the aim of hypouricaemic therapy is to maintain the serum urate level below 0.36 mmol/L. Maintaining urate level below 0.36mmol/L also improves rate of tophi regression and reduces the chance of tophaceous re-deposition.

Uses in Other Clinical Settings:

• Assessment of pre-eclampsia (note that changes within the reference interval can be significant)
• Assessment of metabolic syndrome
• Evaluation of syndrome of inappropriate anti-diuretic hormone (including those on diuretics)
• Monitor tumour lysis syndrome
• Investigation of inborn errors of metabolism
• Assessment of risk of renal stone formation

Reference Intervals

Conversion factors:  mg/100 mL x 0.0598 = mmol/L
mmol/L x 16.722 = mg/100 mL