Version July 2025
| Noninflammatory (such as osteoarthritis) | Inflammatory (such as rheumatoid arthritis) | Septic | Hemorrhagic | |
| WBC count (cells/microL) | <2000 | 2000 to 20,000 | >20,000* | Up to 1 WBC for every 1000 RBCs |
| Neutrophils (%) | <25% | 50 to 75% | >75% | <50%¶ |
| Crystal examination by polarized microscopy | Negative | May demonstrate uric acid or CPPD crystals | Negative | Bloody |
| Stain, culture for microorganisms | Negative | NegativeΔ | May be positive (depending on organism, prior antibiotic exposure) | Negative |
CPPD: calcium pyrophosphate dihydrate deposition; RBC: red blood cell; WBC: white blood cell.
* With most bacterial organisms, particularly Staphylococcus aureus, the synovial fluid WBC count is typically >50,000 cells/microL (and often >100,000 cells/microL). However, lower counts (in the inflammatory range) may be observed in the setting of septic arthritis, especially for disseminated gonococcal infection or if antibiotics were administered prior to joint fluid sampling.
¶ Hemorrhagic synovial fluid usually has <50% neutrophils; however, in some cases a higher proportion may be observed, reflecting the peripheral neutrophil count.
Δ Inflammatory findings are typically observed in the setting of rheumatologic conditions and crystal-induced arthritis; however, concomitant infection also warrants consideration, and synovial fluid culture should be obtained routinely during synovial fluid analysis. In the setting of noninfectious inflammatory arthritis, synovial fluid leukocyte counts may be >20,000 cells/microL (often termed "pseudoseptic"). In general, the higher the synovial fluid leukocyte count, the greater the concern for septic arthritis.
