Levels of GFR and Protein-induced Hyperfiltration in Kidney Donors: A Single-Center Experience in India

Background

Some studies have shown that the normal range of glomerular filtration rate (GFR) was lower in an Indian population than in western populations. To verify these findings and determine whether it is physiological or an expression of subclinical disease, we measured GFR in a cohort of healthy Indian adults by using more stringent criteria to define “healthy” than used in previous studies.

Study Design

Cross-sectional study.

Setting and Participants

109 healthy adults being evaluated for kidney donation with normal blood pressure, body mass index, urinalysis results, and protein excretion and symmetrical function on radionuclide renogram. Subjects followed a vegetarian diet with 1 g/kg of protein intake for 10 days before the study.

Predictors

Age, sex, relation to recipient (relative versus spouse), body surface area, body mass index, kidney size, serum creatinine level, and urinary protein-creatinine ratio.

Outcome and Measurements

GFR measured as plasma clearance of technetium 99m diethyl-triamine-penta-acetic acid before and after amino-acid infusion (protein-induced hyperfiltration). Measurements were performed after a 12-hour fast.

Results

Mean baseline GFR was 82.4 ±12.7 mL/min/1.73 m² (95% confidence interval, 80.0 to 84.8). Mean stimulated GFR was 104.7 ± 16.1 mL/min/1.73 m² (95% confidence interval, 101.6 to 107.8). Measured mean protein-induced hyperfiltration was 27.3% ± 10.04% (range, 6.7% to 56%). In multivariable linear regression analysis, younger age, spousal donor, and larger average kidney size were associated with significantly greater baseline GFR, and only greater baseline GFR was associated significantly with stimulated GFR.

Limitations

Dietary protein intake was not measured; a habitual low-protein diet cannot be excluded as a cause of low GFR.

Conclusions

Basal GFR is significantly lower than the normal value of 120 to 130 mL/min/1.73 m² in western populations. The conventional cutoff value of 60 mL/min/1.73 m² for defining chronic kidney disease might not be appropriate in India.

Index Words: Glomerular filtration rate, Indian adults, protein-induced hyperfiltration, amino-acid infusion