Medical Malpractice Insurance for orthopaedic surgeons
Home » Arthritis » Laboratory Studies for Gout

Laboratory Studies for Gout

 - Hyperuricemia:
         - biochemical hallmark of gout is hyperuricemia, but not by itself diagnostic for gout;
         - also note that the uric acid level can flucuate over wide levels over short periods of time (dont assume that a normal uric acid level
                from 2 days ago represents a constant level);
         - risk of gout increases with the degree and duration of hyperuricemia;
         - more than 95% of pts w/ gout have primary hyperuricemia;
                - these pts exhibit overproduction of endogenous urate regardless of dietary intake;
                - pts w/ primary gout also have defect excreting urate;
         - note that the presence hyperuricemia in a patient with arthritis does not necessarily establish the dx of gout;
         - w/ serum urate concentrations of 9.0 mg per deciliter (540 µmol / lit), incidence of acute gout is only about 5 % / year;

 - Leukocytosis:
         - there may be a left shift of immature PMNs & elevated crp and sed rate; (often the CRP will be much more elevated than the sed rate);
 - Synovial Fluid:
         - synovial fluid leukocyte counts may approach counts seen in septic arthritis;
                - ref:  Markedly Elevated Intra-articular White Cell Count Caused by Gout Alone
         - viscosity of synovial fluid is < that seen in septic or inflammatory arthritis;
         - crystals:
               - crystal examination of synovial fluid:
               - needle-like intracellular & extracellular monosodium urate crystals are seen under compensated polarized light microscopy;
                     - crystals are brightly birefringent and have negative elongation
                     - dx is made by observing negatively birefringent, needle-shaped MSU crystals engulfed by PMNs;
 - Urine Analysis:
         - note that the excretion rate of urate in these patients is usually within the normal range
         - references:
                - Renal function in gout; with a commentary on the renal regulation of urate excretion, and the role of the kidney in the pathogenesis of gout. 
                - Uric acid excretion in patients with gout.