A novel use of attenuation value (Hounsfield unit) in non-contrast CT: diagnosis of urinary tract infection.

Abstract

To investigate the utility of attenuation value (Hounsfield unit) of the filled bladder on computed tomography (CT) images and the association of these values with simultaneously obtained urine culture results. Between January 2016 and December 2017, retrospective data of 58 patients who were admitted to the emergency department for various symptoms were examined. All patients were evaluated with urine dipstick microscopy, urine culture, and abdominal CT simultaneously. Group 1 consisted of patients with positive urine culture (n = 28) and Group 2 consisted of patients with negative urine culture (n = 30). The attenuation value of urine in the bladder at the level of the bladder trigone was measured inside an elliptical drawing covering all the urine inside the bladder excluding the bladder wall on axial non-contrast CT images. The predictive value of this calculated attenuation value for urine culture positivity was evaluated. The median attenuation value was - 6 (range - 17.8 to + 11) and 12 (range 0-32) in group 1 and group 2 (p < 0.001). According to cut-off value of - 1 attenuation value, sensitivity for predicting urine culture positivity was 92.9%, whereas specificity was 100% (AUC: 0.977 p < 0.001). Urine culture was positive in all of the 26 patients with attenuation value < - 1, whereas only two of the 32 patients with attenuation value > - 1 had urine culture positivity (p < 0.001 OR 14). The attenuation value of the urine in the defined area of the bladder may aid in the diagnosis of urinary infection with high sensitivity and specificity and without any additional cost.