This paper will review some fundamentals of normal renal physiology necessary to understand the changes occurring with age and enable the reader to distinguish between chronic renal insufficiency and the consequences of normal ageing on kidney function.

SummaryThis paper reviews the handling of water and electrolytes by the ageing kidney and the clinical consequences in everyday clinical practice. Normal physiology in the adult kidney is discussed, followed by description of the main physiological changes (adaption) that occur as the kidney ages. Clearly, successful management of the elderly patient requires a knowledge of these changes, which result in: (i) increased tendency for volume depletion and dehydration; (ii) decreased ability to tolerate a volume load; (iii) increased propensity for potassium disturbances (hypo- and hyperkalaemia); (iv) diminished production of renin and blunted physiological response to the effects of aldosterone and antidiuretic hormone; (v) increased tendency to lower levels of phosphate; and (vi) tendency for the development of hypocalcaemia and hypomagnesaemia. A brief review of the role of extracellular fluid volume depletion and other factors contributing to acute renal failure in elderly patients is also presented.