To study whether early leukocytosis after total joint arthroplasty (TJA) requires further workup to exclude infection by observing changes in peripheral blood white blood cell (WBC) count after TJA.

This study included the 294 patients (infection-free group) who had undergone primary hip or knee TJA from June 2019 to June 2020 but reported no periprosthetic joint infection (PJI) within one month after surgery and the 31 patients (infection group) who had undergone the same TJA but reported infection within one month after surgery from May 2012 to June 2020 at Department of Joint Surgery, The First Affiliated Hospital to Xinjiang Medical University. Peripheral blood WBC counts were measured and recorded before surgery and 1 to 5 days after surgery. Differences were compared between time points and multiple linear regression analysis was used to screen the factors associated with early postoperative leukocytosis. The receiver operating characteristic (ROC) curve was used to evaluate the predictive value of WBC for early PJI.

The peripheral WBC level in the infection-free group showed a trend of increasing at first and then decreasing. It reached the peak on day 2 after surgery, increasing by 8.08×10⁹/L±2.33×10⁹/L compared to pre-surgery, and then began to decrease to a level slightly higher than the preoperative value on day 5 after surgery. The changes in WBC count in the first 2 days after surgery ranged from 6.24×10⁹/L to 26.32×10⁹/L. The incidence of leukocytosis in the first 5 days after surgery was 95.6% (281/294). The factors associated with postoperative leukocytosis included preoperative WBC count and bilateral surgery. For every increase of 1.00×10⁹/L in preoperative WBC count, the postoperative WBC value increased by an average of 0.98×10⁹/L [β=0.984, 95% confidence interval (95%CI): 0.821-1.148, P<0.001]. The postoperative WBC count in the patients undergoing bilateral surgery increased by an average of 1.03×10⁹/L compared with that in the patients undergoing unilateral surgery (β=1.026, 95%CI: 0.565-1.486, P<0.001). The area under the curve (AUC) for prediction of early PJI by absolute WBC count difference (the absolute difference between the maximum postoperative WBC value and the baseline) was 0.655 (95%CI: 0.546-0.764, P<0.05), providing a threshold of 7.96×10⁹/L, a sensitivity of 57.5% and a specificity of 74.2%.

Leukocytosis is a common phenomenon after TJA, indicating a normal physiological response to surgery. The preoperative WBC count is a predictor for postoperative leukocytosis. In the absence of abnormal clinical symptoms or signs, there is no need for further workup to check infection if the postoperative WBC does not deviate from its changing range and trend.

Arthroplasty, replacement; Hip, knee; White blood cell; Infection