Analysis for crystals in synovial fluid: training of the analysts results in high consistency

• Published in: Annals of the rheumatic diseases 2005-04, Vol.64 (4), p.612-615
• Main Authors: Lumbreras, B, Pascual, E, Frasquet, J, González-Salinas, J, Rodríguez, E, Hernández-Aguado, I
• Format: Article
• Language: English
• Subjects: Arthritis - diagnosis; Biological and medical sciences; Biomarkers - analysis; Calcium Pyrophosphate - analysis; calcium pyrophosphate crystals; calcium pyrophosphate dehydrate; Chondrocalcinosis - diagnosis; Clinical Competence; CPPD; Crystallization; Diseases of the osteoarticular system; Education, Medical, Continuing - methods; Extended Report; Fluids; gout; Gout - diagnosis; Humans; Laboratories; Light; Medical sciences; Metabolic diseases; Microscopy, Polarization; Miscellaneous. Osteoarticular involvement in other diseases; monosodium urate; monosodium urate crystals; MSU; Observer Variation; Other metabolic disorders; Prospective Studies; Purines and pyrimidines (gout, hyperuricemia...); Quality control; Rheumatism; Rheumatology - education; Sensitivity and Specificity; Spain; Studies; Synovial Fluid - chemistry; synovial fluid analysis; Training; Uric Acid - analysis
• ISSN: 0003-4967; 1468-2060
• DOI: 10.1136/ard.2004.027268

Background: Identification of monosodium urate (MSU) and calcium pyrophosphate dehydrate (CPPD) crystals in synovial fluid samples is diagnostic of gout and CPPD crystal related arthropathy. Various studies have shown poor consistency in results of crystal analysis. Objective: To determine whether training of the analysts increases the consistency. Methods: An expert rheumatologist gave a course on crystal detection and identification. The four trained observers then blindly and independently examined synovial fluid samples previously classified by the expert which had been obtained from patients with both crystal arthropathies and other non-crystal related inflammatory joint conditions. Results: 194 observations were made on 64 synovial fluid samples: 96 without crystals (49.4%), 55 with CPPD crystal (28.4%), and 43 with MSU crystals (22.2%). For crystal detection (presence or absence of crystals), sensitivity was 95.9% and specificity 86.5%. For identification of MSU crystals, sensitivity was 95.3% and specificity 97.2%. For identification of CPPD crystals, sensitivity was 92.7% and specificity 92.1%. The κ index of agreement with the reference standard between the observers was 0.84 for any crystal detection, 0.93 for MSU crystal sample identification, and 0.79 for CPPD crystal sample identification. Conclusions: For trained observers, the detection and identification of crystals in synovial fluid is a consistent procedure.