Diagnostic accuracy of radiolabelled-WBC scintigraphy in patients with antibiotic therapy

The aim of this retrospective study was to assess to what extent antibiotic therapy impacts the accuracy of ⁹⁹ᵐTc-HMPAO labelled white blood cell (WBC) scintigraphy. We analyzed 1016 patients who performed WBC scintigraphy, according to EANM guidelines, between May 2014 and September 2025. Only patients with a definite final diagnosis were enrolled (484 patients). Patients were stratified into six groups based on antibiotic therapy status at the time of examination: 1) ongoing antibiotic therapy, 2) discontinued for ≤ 7 days, 3) discontinued for 8–15 days, 4) discontinued for 16–30 days, 5) discontinued for > 30 days or 6) without antibiotic therapy. Overall, we observed a sensitivity of 66%, a specificity of 97% and 86% of accuracy. Sensitivity was markedly reduced in patients receiving antibiotics at the time of testing (30%) and increased according to therapy withdrawal time, reaching 100% in groups 4 and 5. A similar trend was observed for accuracy and NPV. Since we found no difference between groups 1, 2 and 3, these were grouped together and compared to groups 4, 5 and 6 grouped together. The best performance, in terms of sensitivity, specificity, accuracy and NPV was achieved in patients who were not receiving treatment or who had stopped treatment for more than 15 days ( p < 0.0001). Results of this study indicate that the accuracy of radiolabelled WBC scintigraphy is influenced by ongoing antibiotic therapy. Based on our results, 15 days of suspension are advisable to perform WBC scintigraphy.