Hence, most subjects probably had normal kidney function or CKD stages 1 3. CKD in the elderly. There are clear differences in the causes of CKD when comparing elderly and younger cohorts.375 Autopsy studies indicate that arteriolar sclerosis, global glomerulosclerosis, and tubular atrophy are more common in the elderly, as are renal artery stenosis and cholesterol Although selection bias is likely, a kidney biopsy series of 413 patients aged 66 to 79 years and 100 patients aged 80 to 89 years showed nephrosclerosis in 34% of patients 480 years and in 7% of those 66 to 79 yrs.356 According to registries of kidney failure patients, arterio- pathic disease was the diagnosis in 17 to 38% of patients commencing dialysis on three continents.375 Although a discussion as to whether or not nephrosclerosis is an aspect of kidney aging is beyond the scope of this Guideline, vascular disease within the kidney is often regarded as a major factor contributing to decline in kidney function. This predisposi- tion to vascular disease may influence the response of the aging kidney to low BP and renin angiotensin blockade, with the attendant risks of acute reduction in GFR and hyperkalemia. This has led to questions regarding the safety of renin angiotensin-blocking agents such as ACE-Is and ARBs in the elderly.377 379 GFR estimation in the elderly. Most equations used to estimate GFR have been primarily developed in younger populations, although subgroup analyses show that these equations perform reasonably well in older people380,381 . Co-morbidities. Co-morbidities are frequently present in the elderly and may influence BP management. Macrovascular disease is particularly common. This might influence BP targets or the preferred agents use to control BP, especially if heart failure, angina, cerebral vascular insufficiency, or peripheral vascular diseases are prominent. 