- Patients from 18 through 80 years of age who had chronic renal insufficiency were eligible if they had a serum creatinine concentration between 1.5 mg per deciliter (132.6 μmol per liter) and 3.9 mg per deciliter (344.8 μmol per liter), with a decrease in the glomerular filtration rate of less than 5 ml per minute over a period of at least six months