Uric Acid Nephropathy Workup

Updated: Sep 10, 2019
  • Author: Mark T Fahlen, MD; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Workup

Laboratory Studies

Hyperuricemia is an important finding; urate levels in the plasma often exceed 15 mg/dL and can peak as high as 50 mg/dL. However, tumor lysis syndrome in the context of normouricemia has been reported. [21] Progressive azotemia and hyperphosphatemia are other important findings.

An increased serum lactate dehydrogenase level is suggestive of a large tumor burden and correlates with risk.

Urinalysis results are usually bland. Uric acid and sodium monourate crystals may be observed. Although variable, uric acid levels in the urine may be as high as 150-200 mg/dL. A random ratio of urinary uric acid to creatinine higher than 1 is also suggestive of acute uric acid nephropathy. A disproportionate elevation in serum uric acid levels also can be a diagnostic clue.

Elevated serum and urinary uric acid levels correlate with the frequency of nephrolithiasis, and 50% of patients with serum uric acid levels greater than 13 mg/dL or urinary uric acid secretion higher than 1100 mg/d will form stones. Uric acid stones are radiolucent, and the urinary uric acid crystals are reddish-orange. Urate crystals have several forms but tend to be needle-shaped or flat, square plates; both are strongly birefringent.