Overall, renal mass, renal blood flow, tubular function, and glomerular filtration rate (GFR) are all reduced with age. The mass of the kidney decreases by 20-25% between the age of 30 and 80 years (McLean and Couteur 2004). There is a gradual increase in blood urea nitrogen by approximately 0.2 mg/dl per year. Interestingly, despite these changes, serum creatinine concentration remains largely unchanged. This is attributed to the proportional decrease in lean body mass and creatinine production in the elderly population (Prough 2005).
GFR declines by less than 1 ml/min/yr after middle age. As old age is also associated with increased rates of hypertension, vascular disease, and diabetes, it is difficult to accurately predict to what extent decrease in GFR is purely related to age. Additional changes include a blunted renin-angiotensin-aldosterone system (RAAS) response, increased antidiuretic hormone (ADH) levels, and increased atrial natiuretic peptide (ANP) release, especially in the perioperative period (Morgan et al. 2007, Prough 2005).
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