Body fat predicts urinary tract infection in kidney transplant recipients: a prospective cohort study

The association between obesity and infectious diseases is increasingly reported in the literature. There are scarce studies on the association between obesity and urinary tract infection after kidney transplantation (KTx). These studies defined obesity based on body mass index, and their results were conflicting. The present study aimed to evaluate this association using bioelectrical impedance analysis for body composition evaluation, and obesity definition.

A single-center cohort study was conducted. Demographic, clinical, anthropometric, and laboratory data were collected at KTx admission, and bioelectrical impedance analysis was performed to measure the visceral fat area, waist circumference, and total fat mass. The occurrence of urinary tract infection (symptomatic bacteriuria and/or histological evidence of pyelonephritis) was evaluated within three months after KTx.

Seventy-seven patients were included in the cohort, and 67 were included in the final analysis. Urinary tract infection was diagnosed in 23.9% of the transplanted patients. Waist circumference (HR: 1.053; 95% CI 1.005-1.104; p = 0.032), visceral fat area (HR: 1.015; 95% CI 1.003-1.027; p = 0.014), and total fat mass (HR: 1.075; 95% CI 1.008-1.146; p = 0.028) were associated with urinary tract infection occurrence after KTx, using Cox regression models. Patients with high waist circumference (above 102 cm for men and above 88 cm for women) had a 4.7 times higher risk of a urinary tract infection than those with normal waist circumference (HR: 4.726; 95% CI 1.267-17.630; p = 0.021). Kaplan-Meier curves showed that patients with high waist circumference, high visceral fat area, and high total fat mass had more urinary tract infections (Log-rank test p = 0.014, p = 0.020, and p = 0.018, respectively). Body mass index was not able to predict urinary tract infection in the study sample.

Waist circumference, visceral fat area, and total fat mass, assessed by bioelectrical impedance analysis, were predictors of urinary tract infection risk within the first three months after KTx.