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Renal size depends on several factors and anthropometric variables like height, BMI and gender. Race is also important due to its relation with these variables. Glomerular filtration rate (eGFR) declines with aging, decreasing at rate of 0.8ml/minute/1.73m2/year after age 30 due to parenchymal sclerosis with decreased kidney size. Renal size is also altered with pathological causes of sclerosis, like glomerulopathies. This study describes the variation in kidney size resulting from the involvement of the glomerular and tubulointerstitial compartments and between different anthropometric variables.
Patients older than 18 years, biopsied at Fernandez Hospital Nephrology Unit from June 2021 to June 2023 were included (n=383 cases, 247 women) in this prospective study. Patients with ESRD stage 4 were excluded. Kidney measurement was performed by ultrasound that was always done by the same operator. The biopsied kidney was the left one in 98 % of the cases. The following items were analyzed: age, gender, weight, height, body surface, BMI, biopsied kidney length (BxKL), cortical thickness, degree of glomerular (GS) and tubulointerstitial sclerosis (TIS). eGFR was calculated with CKD-EPI creatinine equation.
All data are expressed as mean (sd) otherwise indicated. Simple and multiple linear regression analysis were carried-out to assess the association between renal length and several explanatory variables. A p value <0.05 was assumed as statistically significant.
The mean age of the patients was: 39.0± 0.7 years, weight: 61.3± 0.8 Kg, height: 162± 4 mm, body surface: 1.8±0.01 m2, BMI 26.84±0.3, eGFR: 92.7± 2.6ml/min, BxKL: 103.2± 6mm: women 101.8±5mm and men 105.9±8mm, cortical thickness: 15.6± 0.2mm, tissue degree of GS: 20± 1.1% and TIS: 13.3± 0.6%.
A significant (P< 0.05) relationship was found between BxKL and the following parameters: height, weight, length between men and women, BMI, cortical thickness and eGFR. Also, the cortical thickness showed a significative concordance with eGFR and GS but not with TIS.
Relationship between height and BxKL in patients without GS or TIS was noteworthy (P <0.001); meanwhile in those patients with renal fibrosis a minor kidney length was related to higher GS or TIS grade (P <0.05). BxKL was also associated with the age in women (P <0.05), but this was not significative in men.
Kidney length assessed by ultrasound is significantly correlated with height, weight, BMI, cortical thickness, age (only in women) and eGFR. Nevertheless, in those patients with renal fibrosis, its length diminishes at the increase of GS and/or TIS.
The smaller kidney size found in our population (103,2±6mm) compared to other published studies (112±9mm for left kidney) could be due to ethnic differences and because in this study most of the patients (64,4%) were women. Unexpectedly, cortical thickness kept its relationship between eGFR and glomerular sclerosis, but not with tubulointerstitial lesions.