Regression equation for kidney function based on the ultrasonographic volumetry of the renal cortex

Chronic kidney disease (CKD) is a public health concern; kidney size correlates with kidney function, except in diabetic kidney disease (DKD), where the kidney enlarges, limiting morphological measurement applications in CKD management. However, cortical size changes in DKD along with CKD progression remain understudied. We investigated kidney morphology alterations in patients with and without diabetes and established a regression equation for kidney function incorporating morphological alterations.

We included 312 patients who underwent kidney morphological measurements at Tottori University Hospital between 2018 and 2024. After excluding 34 subjects, 278 patients were divided into derivation and validation groups. Ultrasonography was used to assess kidney morphology including parenchymal, cortical, and medullary thicknesses, length, and kidney and cortical volumes. The non-diabetic and diabetic groups were compared at each CKD stage. Multivariate linear regression generated renal function equations.

In the derivation group (247 patients), height-adjusted cortical volume was strongly associated with kidney function in patients without diabetes (r = 0.513, p < 0.001) and with diabetes (r = 0.701, p < 0.001). Cortical volume was significantly larger in patients with than in those without diabetes at each CKD stage, except stages 4 and 5. In the validation group (31 patients), the predicted estimated glomerular filtration rate (eGFR) strongly correlated with the actual eGFR (r = 0.803, p < 0.001).

A strong correlation between cortical size and kidney function was observed. Cortical size alterations depended on the cause of CKD. A regression equation incorporating kidney size can help assess the eGFR. These findings could help formulate strategies for improving CKD management.