Kleeman-Forsthuber LT, Dennis DA, Brady AC, et al. - Diagnostic accuracy of periprosthetic joint infection (PJI) following total knee (TKA) and hip (THA) arthroplasty may improve with synovial fluid alpha-defensin (AD) but it is only available as a send-out test. Researchers here examined the accuracy of laboratory results between send-out test vs hospital labs and determined if AD modifies treatment plan. They retrospectively reviewed 152 consecutive patients with a TKA or THA joint aspiration for painful or clinically concerning joint. Synovial fluid was sent to the institution (hospital-based labs, HBL) and sent-out to the immunoassay laboratory (Synovasure). Outcomes revealed that laboratory values between institutions had minimal differences. The AD test modified the PJI diagnosis and affected decision for surgery in only 1.3% (2/152) of patients. Overall findings suggest that in cases of equivocal laboratory results, the addition of AD may be relevant but does not seem to be imperative for routine diagnosis of PJI after TKA/THA.