Levels of serum creatinine and estimated creatinine clearance over the age of 75: a study of an elderly Swedish population

Serum creatinine was measured and creatinine clearance estimated using the Cockcroft-Gault (C-G) formula, in elderly people participating in a population study of the elderly, the Kungsholmen Project. This is an ongoing longitudinal study which was begun in 1987 and comprised all people in a district of Stockholm, born in 1912 or earlier. Out of 2368 people 1810 participated. In 1362 cases, serum creatinine and an estimation of the creatinine clearance could be obtained. The mean age of these elderly people was 81 years, and 92% were living in their own homes. A linear regression model showed that the weight of the elderly decreased by age, indicating a decrease in muscle mass. However, this was not accompanied by a decrease in serum creatinine levels. When creatinine clearance was estimated using the C-G formula, a significant decline with age was seen at an average rate of 1.2 ml/min per year. It declined from 52 ml/min at age 75 to 27 ml/min at age 95. The mean for the whole study group was 44.6 ml/min. Our data suggest that the glomerular filtration rate may be very low in the oldest old and that there is a continuing decline with increasing age, even in a population where a high number of the elderly are still living in their own homes. Furthermore, the lack of major changes in serum creatinine levels with age supports the idea that this parameter is not a reliable measure of renal function in the elderly.