Reproducibility of synovial fluid examination for crystals.

A quality assurance survey of synovial fluid examination for crystals was performed at six teaching hospitals. Aliquots of 12 different fluids (three with no crystals, one with betamethasone crystals, four with calcium pyrophosphate dihydrate (CPPD) crystals and four with monosodium urate monohydrate [urate] crystals) were examined by all six laboratories. Four laboratories performed well (10 or more correct out of 12) but two did poorly (50% or less correct). False positive crystal identification occurred in eight of 72 samples, but all false positive reports were from two laboratories. CPPD and urate crystals were missed in seven of 24 (29%) and five of 24 (21%) samples respectively. The standard of synovial fluid examination for crystals in Sydney teaching hospitals is not uniform and in some cases appears unsatisfactory.