An equation to estimate the renal cortex volume in chronic kidney disease patients.

Background: The renal cortex volume is associated with the kidney function and chronic kidney disease (CKD) risk factors, and it may also be a prognostic factor. We aimed to create an equation to estimate the renal cortex volume of CKD patients in day-to-day clinical practice.

Methods: The subjects included 116 ethnic Japanese CKD patients who were ≥ 18 years of age. The renal size (length, width and thickness) was measured by ultrasound. The body height, weight, year of age, sex, birth weight, gestational age, diabetes status, hypertension status, family history of CKD and dialysis and estimated glomerular filtration rate (eGFR) were collected as expected dependent variables. We made models for the equation regarding the renal cortex volume measured by non-contrast magnetic resonance imaging as a true renal cortex volume. Stepwise multiple linear regression analyses were performed with the log-transformation of dependent and independent variables. The accuracy of the models was compared using the leave one out cross-validation method.

Results: The estimated volume of the renal cortex (cm) = 0.012 × renal length (cm) × width (cm) × body weight (kg) × body height (cm) × eGFR (ml/min/1.73 m) × 1.12 if diabetes. The adjusted R value and the accuracy within 30 and 50% were 0.73, 0.94 and 0.99, respectively.

Conclusions: This study provided a new method for estimating the renal cortex volume in day-to-day clinical practice.