A diagnostic rule for acute gouty arthritis in primary care without joint fluid analysis.

BACKGROUND Most cases of acute gouty arthritis are diagnosed in primary care and without joint fluid analysis in many instances. Our objectives were to estimate the validity of this diagnosis by family physicians and to develop a diagnostic rule. METHODS Patients with monoarthritis recruited in an open Dutch population with gout by family physician diagnosis were enrolled in a diagnostic study (March 24, 2004, through July 14, 2007). Validity variables were estimated using 2 x 2 tables, with the presence of synovial monosodium urate crystals as the reference test. For development of the diagnostic rule, clinical variables (including the presence of synovial monosodium urate crystals) were collected within 24 hours. Statistically significant variables and predefined variables were separately entered in multivariate logistic regression models to predict the presence of synovial monosodium urate crystals. Diagnostic performance of the models was tested by receiver operating characteristic curve analysis. The most appropriate model was transformed to a clinically useful diagnostic rule. RESULTS Three hundred twenty-eight patients were included in the study. The positive and negative predictive values of family physician diagnosis of gout were 0.64 and 0.87, respectively. The most appropriate model contained the following predefined variables: male sex, previous patient-reported arthritis attack, onset within 1 day, joint redness, first metatarsophalangeal joint (MTP1) involvement, hypertension or 1 or more cardiovascular diseases, and serum uric acid level exceeding 5.88 mg/dL (to convert serum uric acid level to micromoles per liter, multiply by 59.485). The area under the receiver operating characteristic curve for this model was 0.85 (95% confidence interval, 0.81-0.90). Performance did not change after transforming the regression coefficients to easy-to-use scores and was almost equal to that of the statistically optimal model (area under the receiver operating characteristic curve, 0.87; 95% confidence interval, 0.83-0.91). CONCLUSIONS The validity of family physician diagnosis of acute gouty arthritis was moderate in this study. An easy-to-use diagnostic rule without joint fluid analysis was developed for their use.