This study intends to determine the diagnostic value of implementing a corrective formula that can adjust for serum leukocytes in bloody joint fluid. Our cohort included 91 infected and 37 aseptic total knee arthroplasties. Joint fluid leukocyte count (>1760/μL) and neutrophil percentage (>73%) were the cutoff values for deep infection. The adjusted fluid leukocyte counts were calculated using the following simple formula: WBCadjusted = WBCobserved - [(WBCblood × RBCfluid/RBCblood)]predicted. Adjusted fluid cell counts of only 5 infected patients dropped below the cutoff value, whereas the remaining 86 maintained a high cell count. Ten noninfected patients had false-positive cell counts, 6 of which were successfully corrected to levels below the designated thresholds. The aspirates that were corrected had a greater number of introduced white blood cells. This study suggests that our corrective formula can detect false-positive joint aspirations without jeopardizing the diagnosis of periprosthetic infection. © 2008 Elsevier Inc. All rights reserved.