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NewsThink twice before relying on a single lab test to diagnose prosthetic joint infections. A new audit found that synovial fluid white blood cell count and PMN percentage — currently allowed as standalone rule-in tests under major PJI guidelines — are actually poor solo diagnostics. Roughly one in three positive results could flag a patient who isn't actually infected, raising serious concerns about overdiagnosis and unnecessary treatment.
Think twice before relying on a single lab test to diagnose prosthetic joint infections.
A new audit has challenged the diagnostic standards set by the Unified Periprosthetic Joint Infection (PJI) Criteria and the 2021 European Bone and Joint Infection Society, both of which allow synovial fluid white blood cell (WBC) count and polymorphonuclear (PMN) percentage to serve as standalone rule-in tests for PJI. Researchers at Rothman Orthopaedic Institute reanalyzed the 2025 meta-analysis underpinning these guidelines and found significant methodological flaws — including swapped data columns, biased threshold selection, and high heterogeneity across studies — that inflated the tests' apparent accuracy.
When corrected, the numbers told a different story: at a 20% PJI prevalence, roughly one in three positive results would occur in a patient without an actual infection.
By the Numbers:
Why it matters: Using either test alone to confirm PJI could lead to patients being diagnosed and treated for an infection they don't have. Experts stress these tests remain valuable — but only as part of a broader, multimodal diagnostic workup that includes cultures, serum markers, and clinical context.
