Single tests are not very reliable in differentiating causes in patients with acute hot joints

Reference

Dey M, Al-Attar M, Peruffo L, et al. Assessment and diagnosis of the acute hot joint: a systematic review and meta-analysis. Rheumatology (Oxford) 2023;62(5):1740-1756.

Synopsis

These authors searched several databases and registries to identify English-language studies that evaluated patients of any age with hot swollen native joints with onset less than 6 weeks before enrollment. They included 49 studies with sample sizes ranging from 6 to 1161 patients. The studies had to use one or more serum or synovial fluid markers compared with a reference standard of clinical assessment plus joint fluid microscopy and culture. Overall, the studies were of mixed quality; some were at low risk of bias for all domains, while others were ... not. To identify patients with septic arthritis, the authors found studies that evaluated several serum tests (procalcitonin, erythrocyte sedimentation rate [ESR], C-reactive protein [CRP], white blood cell [WBC] count, uric acid, TIMP-1, CTX-II, and calprotectin). Of those tests, procalcitonin (using 10 µg/L), TIMP-1, and CTX-II were very specific (values from 0.89 - 1.0), but not very sensitive (0.087 - 0.727). Conversely, ESR and CRP are quite sensitive, but not very specific. Synovial fluid tests (glucose, lactate, leucocyte esterase, polymorphonuclear leucocytes, procalcitonin, tumor necrosis factor-alpha, and WBC count) varied widely (sensitivity ranged from 0.36 - 0.94 and specificity from 0.65 - 0.99). The leucocyte esterase assay was most sensitive (++ or +++; 0.94) and lactate was most specific (10 mmol/L or higher; 0.99). The authors identified only 2 studies, each using synovial fluid tests, for distinguishing crystal from non-crystal arthritis. Crystal analyses (monosodium urate and calcium pyrophosphate) were sensitive (0.89 and 0.93, respectively) and specific (1.0 and 0.88, respectively). Finally, because of variable definitions of inflammatory arthritis and the heterogeneity of study designs and thresholds, the authors did not report data on tests for identifying patients with inflammatory arthritis.