Serum and Synovial Uric Acid Validated as Markers for Osteoarthritis

The amount of uric acid in the synovial fluid of the knee is strongly correlated with the severity of osteoarthritis and the progression of the disease over time.

The amount of uric acid in both serum and synovial fluid can be estimated using high performance liquid chromatography (HPLC) and correlated with the severity of debilitating joint degeneration found in patients with osteoarthritis (OA).

A study carried out at Duke University Medical Center (Durham, NC, USA) examined 159 (118 females, 41 males) patients, who had knee osteoarthritis but no history of gout, a type of arthritis triggered by uric acid crystals in the joints. A total of 138 participants returned for follow-up three years later to assess progression of knee OA. The study was conducted from January 2003 until March 2008. Serum and knee synovial fluid samples were obtained within 10 minutes of each other after a two hour fast in the mid-afternoon. The synovial fluid analyses were limited to 69 study participants (49 women and 20 men) with sufficient synovial fluid volumes for uric acid analyses.

Although this cohort was recruited based on knee OA and absence of gout history, a surprising 39% of this cohort had serum uric acid concentrations above their respective reference ranges of 7.2 mg/dL for men and 6.0 mg/dL for women. Uric acid was quantified in both knees of 63 participants and single knees of 6 participants, and their paired sera. The mean serum uric acid concentrations were significantly higher than their paired synovial fluid uric acid concentrations. Of the 132 synovial fluid samples, matched serum exceeded synovial fluid uric acid concentrations for 113 (85.6%), whereas only 19 (14.4%) had greater synovial fluid than serum uric acid concentrations.

Virginia Byers Kraus, MD, PhD, professor of medicine at Duke University, said, "We've always thought of uric acid as the agent for gout, but it may be a much more general agent. In a non-gout population, this provides some of the very first evidence that uric acid level is a potential cause of inflammatory events and joint degeneration in osteoarthritis.” The study was accepted for publication on December 10, 2010, in the Proceeding of the [US] National Academy of Science of the United States, (PNAS).

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Duke University Medical Center