- 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.