Background: Renal function is thought to decrease with age in the general population, but the determinants of this age-associated evolution are poorly understood. Hypertension and diabetes mellitus, two leading causes of chronic renal failure in the elderly, may accelerate this decline.
Patients and methods: Urinary clearances of [99mTc]diethylene triaminopentaacetic acid (DTPA) (glomerular filtration rate) and [131I]hippuran (effective renal plasma flow) were assessed in 227 never-treated essential hypertensives aged 20-69 years. Based on the oral glucose tolerance test, the study population consisted of 4% patients with previously unknown diabetes mellitus, 24% with impaired glucose tolerance and 72% with normal glucose tolerance.
Results: When the population of 218 non-diabetic subjects was considered, glomerular filtration rate was inversely correlated with age and arterial blood pressure, and positively correlated with effective renal plasma flow, filtration fraction and fasting plasma glucose. In multivariate analysis, age and blood pressure were independent determinants of renal plasma flow, whereas renal plasma flow, age and fasting plasma glucose were independent determinants of glomerular filtration rate. The slope of the regression line relating glomerular filtration rate to age was steeper in patients with impaired glucose tolerance than in those with normal glucose tolerance (-1.52 +/- 0.28 versus -0.65 +/- 0.12, P < 0.01).
Conclusions: These results suggest that impaired glucose tolerance, which is seldom searched for in patients with essential hypertension, may be an important determinant of the age-associated decline in renal function.