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- Synovial fluid analysis: should be performed to confirm gout even when clinical appearance is strongly suggestive; joint aspiration and demonstration of both intracellular and extracellular needle-shaped negatively birefringent MSU crystals by polarizing microscopy. Gram stain and culture should be performed on all fluid to rule out infection. MSU crystals can also be demonstrated in chronically involved joints or tophaceous deposits.
- Serum uric acid: normal levels do not rule out gout.
- Urine uric acid: excretion of >800 mg/d on regular diet in the absence of drugs suggests overproduction.
- Screening for risk factors or sequelae: urinalysis; serum creatinine, liver function tests, glucose and lipids; complete blood counts.
- If overproduction is suspected, measurement of erythrocyte hypoxanthine guanine phosphoribosyl transferase (HGPRT) and PRPP levels may be indicated.
- Joint x-rays: may demonstrate cystic changes, erosions with sclerotic margins in advanced chronic arthritis.
- If renal stones suspected, abdominal flat plate (stones often radiolucent), possibly IVP.
- Chemical analysis of renal stones.
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