Aging and the kidney: clinical implications.

Beyond the age of 30, kidney size begins to decrease, and there are accompanying decreases in total renal blood flow, outer cortical flow, glomerular filtration rate and the ability both to conserve and to excrete sodium. There is also a decline in concentrating ability and possibly in diluting ability. These changes make the elderly patient more susceptible both to hyponatremic and to hypernatremic states.