Analysis for crystals in synovial fluid: training of the analysts results in high consistency.
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 kappa 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.
Lumbreras
B
B
Department of Clinical Analysis, Hospital General Universitario de Alicante, Spain.
Pascual
E
E
Frasquet
J
J
González-Salinas
J
J
Rodríguez
E
E
Hernández-Aguado
I
I
D001168:Arthritis / Q000175:diagnosis*; D015415:Biomarkers / Q000032:analysis; D002131:Calcium Pyrophosphate / Q000032:analysis*; D002805:Chondrocalcinosis / Q000175:diagnosis; D002983:Clinical Competence; D003460:Crystallization; D004502:Education, Medical, Continuing / Q000379:methods; D006073:Gout / Q000175:diagnosis; D006801:Humans; D008859:Microscopy, Polarization; D015588:Observer Variation; D011446:Prospective Studies; D012219:Rheumatology / Q000193:education; D012680:Sensitivity and Specificity; D013030:Spain; D013582:Synovial Fluid / Q000737:chemistry*; D014527:Uric Acid / Q000032:analysis*
D015415:Biomarkers; D014527:Uric Acid; D002131:Calcium Pyrophosphate