Level of Agreement with the Microscopic Analysis of Joint Aspirate for the Diagnosis of Gout in the Lower Extremity.

Background: Although clinical findings, laboratory serum markers, and radiographic images are also used, the purported gold standard or standard reference test for the diagnosis of gout is microscopic analysis of aspirated joint fluid. This observational investigation sought to identify the level of agreement with the microscopic analysis of joint fluid aspirate for the diagnosis of gout in the lower extremity between two departments in a single health-care center.

Methods: A retrospective medical record review identified consecutive patients seen for suspected gout who underwent diagnostic joint aspiration. Patients were included if a lower-extremity joint synovial fluid sample was obtained and were excluded if they were not independently evaluated by both the departments of rheumatology and pathology. We categorized the documented joint fluid findings into four groups: no crystals, sodium urate crystals, calcium pyrophosphate dihydrate crystals, or both sodium urate and calcium pyrophosphate dihydrate crystals. We defined a "clinically significant disagreement" as one department observing any type of crystals and the other department observing no crystals.

Results: We observed a clinically significant disagreement rate of 23.26% (intraclass correlation coefficient = 0.496). The department of rheumatology was more likely to observe the presence of crystals in a sample compared with the department of pathology (88.37% versus 65.12%; P = .02).

Conclusions: These results provide evidence that microscopic analysis of joint fluid aspirate might lack the accuracy and reliability needed to be considered a gold standard diagnostic test for gout in the lower extremity.