Serum white blood cell count and differential do not have a role in the diagnosis of periprosthetic joint infection.

Serum white blood cell (WBC) count and neutrophil differential are frequently ordered during preoperative workup of suspected cases of periprosthetic joint infection (PJI). However, their roles in diagnosis of PJI have remained unclear despite previous studies. In this study, preoperative serum WBC and neutrophil percentages were retrieved from hospital charts. The diagnostic cutoff point determined by receiver operating characteristic curve analysis was 7800 cells/μL with 55% sensitivity and 66% specificity for WBC count, whereas the cutoff value for neutrophil percentage was 68% with 52% sensitivity and 75% specificity. Our study confirms the long-held belief that serum WBC count and differential has minimal role in routine workup of patients with suspected PJI.