Usefulness of urinary β2-microglobulin for diagnosing acute focal bacterial nephritis

In this study, we aimed to evaluate the usefulness of urinary β2-microglobulin (U-β2MG) for diagnosing acute focal bacterial nephritis (AFBN) among upper urinary tract infections (UTIs). This retrospective study was performed at a single institution and included patients younger than 16 years of age diagnosed with upper UTIs. Patients were divided into the AFBN group and acute pyelonephritis (APN) group. Levels of U-β2MG corrected using urinary creatinine (U-β2MG/Ucre) were compared between groups. A multiple regression analysis was performed using Log(U-β2MG/Ucre) as a dependent factor and the diagnosis (AFBN or APN), age, sex, hydronephrosis grade, urinary pH, and fever interval before admission as independent factors. To discriminate AFBN and APN, thresholds of U-β2MG/Ucre and C-reactive protein (CRP) levels were measured using the receiver-operating characteristic curve. Nineteen patients and 37 patients with AFBN and APN, respectively, were analyzed. The U-β2MG/Ucre level differed significantly between the AFBN and APN groups (10762 μg/gCr vs. 1525 μg/gCr, respectively; P = 0.007). The multiple regression analysis indicated that the Log(U-β2MG/Ucre) value of the AFBN group was considerably higher than that of the APN group (P = 0.004). The threshold values of U-β2MG/Ucre and CRP levels were 2070 μg/gCr and 5.7 mg/dL, respectively. Sensitivity and specificity were 0.95 and 0.68, respectively, when both thresholds were used.Conclusions: The U-β2MG/Ucre level of patients with AFBN was significantly higher than that of patients with APN. Therefore, U-β2MG/Ucre could be used to discriminate between AFBN and APN. What is Known: • U-β2MG can aid in discriminating between upper and lower UTIs; however, using both U-β2MG and procalcitonin allows for more accurate differentiation What is New: • U-β2MG may be useful for discriminating between AFBN and APN in upper UTIs. Assessing both U-β2MG and CRP levels may improve the diagnosis of AFBN without invasive imaging tests.