Effects of age on renal efficiency

Renal efficiency of 70 healthy subjects, 20 young av. age 27.2 +/- 5.8 yrs and 60 elderly av. age 68.2 +/- 4.7 yrs was studied by simple water elimination test in the monitoring under standard conditions. After drinking 2 litre of water, hourly samples of urine upto 4 hrs were collected for volume, sp. gr. urea, creatinine etc. The younger group passed 77% of the extra water drunk in 2 hrs and 92.5% in 4 hrs, whereas the elderly could throw out only 33% in 2 hrs and 56% in 4 hrs. The elderly showed much delayed and poorer elimination. The sp. gr., urea and creatinine in each sample of urine were less in the old indicating their inefficient elimination ability. Av. blood urea was 20.2 +/- 3.8 mg+ in young and 25.4 +/- 7.0 mg% in elderly, respectively. Calculated av. urea clearance value was 61.3 ml/mt in the young, while it was 39.4 ml/mt in the elderly. How well this simple test reflects the decreasing renal efficiency on ageing and compares with more elaborate tests like urea clearance is discussed.