Crystal identification of synovial fluid aspiration by polarized light microscopy. An online test suggesting that our traditional rheumatologic competence needs renewed attention and training.

Testing a reading exercise for identification of several typical crystal such as the negatively birefringent needle-shaped crystals that are under polarized light microscopy is the gold standard for diagnosing gout. The objective of this study was to assess current performance of crystal identification by professionals involved in examining synovial fluid in routine care. Rheumatologists, trainees, lab technicians, and other physicians with an interest in crystal arthritis completed an online test. The test consisted of 30 images: 8 monosodium urate (MSU) crystals, 5 calcium pyrophosphate (CPP), 4 cholesterol, 2 depot methylprednisolone, 2 calcium oxalate, 2 rice bodies, 1 hydroxyapatite, 1 liquid lipid, 1 fibrin, 1 Charcot-Leyden, and 5 different artifacts. Of the 22 non-MSU slides, a subset of 8 was pre-designated that were thought to be clinically important to be identified as non-MSU. The primary outcome was defined as the correct identification of all eight MSU slides plus the identification of all eight pre-defined non-MSU slides as non-MSU. The online test was completed by 110 participants. The primary outcome was achieved by 39%. Correct identification of all MSU images was achieved by 81%, correct identification of all 8 pre-defined non-MSU, CPP images, and all 22 non-MSU images as non-MSU by 68, 68, and 23%, respectively. MSU crystals were well identified, but incorrect identification of non-MSU crystals occurred frequently. This study suggests that there is room for improvement regarding crystal identification of particularly CPP and other non-MSU crystals even in this highly motivated group.