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Glomerular Filtration Rate (GFR) when measured (mGFR) is often found to be low among Living Kidney Donors (LKDs) in India. Isolated finding of low GFR with no other evidence of kidney disease or comorbidities like diabetes or hypertension was the most common reason why LKDs were considered ineligible to donate at our centre. The reason for low mGFR observed in Indians is not clear and multiple factors are proposed to play a role, including low dietary protein intake and low lean body mass. Malnutrition and low birth weight can result in low number of nephrons. There are no reports of number of glomeruli in healthy Indians. Hence this study was conducted to estimate the total number of glomeruli and single nephron GFR among LKDs at our centre.
In a prospective observational study, we enrolled LKDs who underwent donor nephrectomy at our centre. The renal cortical volume of both the kidneys were measured from the pre-donation Contrast Enhanced Computed Tomography images. We calculated the glomerular density from the pre-implantation kidney biopsy by morphometric analysis of needle core biopsy. Glomerular density was corrected for absence of capsule, presence of partially dissected glomeruli , missing glomerular tufts and tissue shrinkage based on validated methodology used in earlier studies. From the total renal cortical volume, glomerular density and the measured GFR, we calculated the total number of nephrons in each kidney and the single nephron GFR.
Thirty-five LKDs were eligible and enrolled in the study. The mean age of the living kidney donors was 43.6±9.93 years. Our study population was heterogenous including LKDs from South and East India. Out of the 35 donors, 29 (82.9%) were females. 14 (40%) LKDs had hypertension (SBP>130 or DBP>80 mmHg) and 13 (37.1%) had prediabetes (IFG, IGT or HbA1c 5.7 – 6.4%). The mean BMI was 24.7±3.07. The mean GFR (CKD-EPI) was 105.97±16.64 ml/min/1.73m2 and mean normalized GFR by DTPA renal plasma clearance was 92.12 ± 14.71ml/min/1.73m2.
The mean total cortical volume was 210,481.7±33570 mm3. The median number of total and non-sclerotic glomeruli among our LKDs were 651,178 (439,726-1,105,129) and 645,833 (439,726-1,098,490) per kidney respectively. The median single nephron GFR was 52.13 (35.06-96.51) nanoliter/min. Among the various independent variables assessed, only serum uric acid had a statistically significant (p value - 0.029) negative association with the number of glomeruli.
The number of total glomeruli and non-sclerotic glomeruli among our LKDs were lower than the number of total glomeruli and non-sclerotic glomeruli reported among American and Japanese LKDs.