Synovial fluid analysis for the enhanced clinical diagnosis of crystal arthropathies in a tertiary care institution

Introduction/objectives: Few studies have addressed the detection and clinical impact of different crystals in patients with diverse rheumatologic diagnoses in Latin America. The aim of this study was to assess the consistency between the clinical referring diagnosis and the identification of crystals, such as monosodium urate (MSU) and calcium pyrophosphate (CPP), in the synovial fluid (SF) of patients from a Mexican tertiary care institution.

Methods: We reviewed the results of 264 SF analyses to identify any changes in diagnosis upon SF analysis. We reported patient medical file data on sex, age, diagnosis, and microscopic SF analysis results. We performed consistency analyses between referring diagnoses and SF findings with McNemar's test.

Results: The prevalence of MSU crystals in SF was noted in 89.1% of gout cases and 9.09% of cases of calcium pyrophosphate disease (CPPD). CPP crystals were present in 54.5% of CPPD cases, 42.9% of osteoarthritis (OA) cases, and 7.27% of gout cases. Calcium hydroxyapatite (HA) crystals were identified in 5.45% of gout cases, 33.3% of rheumatoid arthritis (RA) cases, 57.1% of OA cases, and 63.6% of CPPD cases. Cholesterol and lipid crystals were present in small proportions in RA cases. Glucocorticoid crystals were observed in 1.85% of gout cases, 44.4% of RA cases, and 42.9% of OA cases. We observed an association of MSU identification with clinical suspicion of gout (P = 0.08), CPP with OA (P = 0.26) and CPPD (P = 0.50). An association was noted between HA and the diagnosis of CPPD (P = 0.84) and OA (P > 0.99). The number of initial diagnoses that changed upon SF analysis was 14.3%.

Conclusions: SF analysis has major diagnostic value regarding MSU crystals and gout. Our findings underscore the importance of SF crystal analysis in identifying the prevalence of crystals in the Mexican population. SF analysis provides for better diagnosis of crystal arthropathies and improves the quality of the medical care that the patient receives. Key Points • Synovial fluid analysis in laboratories from developing countries has been scarce. • In some cases, the initial diagnosis is modified after of synovial fluid analysis. • This study confirmed that synovial fluid analysis exhibits major diagnostic value for urate crystals and gout.