Skin-to-Renal Pelvis Distance Predicts Costovertebral Angle Tenderness in Adult Patients with Acute Focal Bacterial Nephritis

Costovertebral angle (CVA) tenderness is an important finding in the diagnosis of acute focal bacterial nephritis. There are no data about the association between the depth of the kidney and CVA tenderness positivity. The authors define skin-to-renal pelvis distance as a parameter of kidney depth and propose that skin-to-renal pelvis distance can be a predictive parameter of CVA tenderness in patients with acute focal bacterial nephritis. Abstract Objectives The aim of this study was to examine whether the distance between the skin and the renal pelvis affects the detection of costovertebral angle (CVA) tenderness in patients with acute focal bacterial nephritis (AFBN). Methods We retrospectively reviewed the charts of our patients between April 2013 and June 2019 who were diagnosed as having AFBN. Diagnosis was based on ultrasound or computed tomography with contrast, revealing at least one wedge-shaped area of decreased vascularity and confirmation of fever not attributable to another condition. Results We extracted 23 cases, all Japanese (mean age 60.0 years old [range 45–81 years], 7 males, 16 females). CVA tenderness was present in 8 of these 23 patients. Receiver operating characteristic curves were drawn to evaluate the ability to differentiate skin-to-renal pelvis distance (SPD), body mass index, and age. Only SPD was a useful predictor of CVA tenderness, and 66 mm was determined as the optimal cutoff point (area under the receiver operating characteristic curve 0.858, 95% confidence interval 0.70–1.00). Logistic regression analysis was performed with CVA tenderness as a dependent variable, and SPD, body mass index, and age as explanatory variables. SPD was an independent predictive variable of CVA tenderness (P = 0.038, odds ratio 0.76, 95% confidence interval 0.590–0.986). Conclusions CVA tenderness showed low yield in the diagnosis of AFBN in patients with longer SPD. Its use for diagnosis in obese patients may therefore be limited.