Synovial Fluid Analysis for Diagnosis of Intercritical Gout

BACKGROUND: The diagnosis of gout in the intercritical phase can be difficult. OBJECTIVE: To determine whether synovial fluid analysis allows the diagnosis of intercritical gout. DESIGN: Cross-sectional study. SETTING: Outpatient rheumatology clinics. PATIENTS: 101 patients with gout. INTERVENTION: Arthrocentesis of 80 knees and 21 first metatarsophalangeal joints (each joint from a different patient) that had been inflamed but were currently asymptomatic. MEASUREMENTS: Frequency with which arthrocentesis yielded synovial fluid; presence of monosodium urate crystals in the synovial fluid sample; and, for synovial fluid with crystals, the number of microscope fields that had to be scanned before crystals were found. RESULTS: Synovial fluid was obtained from 91 of 101 joints. The fluid from all 43 patients not receiving hypouricemic agents contained monosodium urate crystals. These crystals were found in the synovial fluid of only 34 of 48 patients receiving hypouricemic agents. In 90% of the synovial fluid samples that contained crystals, crystals were seen in the first five microscope fields examined. CONCLUSIONS: Arthrocentesis of asymptomatic knees and first metatarsophalangeal joints and synovial fluid analysis are simple procedures that facilitate the diagnosis of gout during intercritical periods.