[Normal ranges of blood urea nitrogen and serum creatinine levels in the community-dwelling elderly subjects aged 70 years or over--correlation between age and renal function].

To estimate normal ranges of blood urea nitrogen (BUN) and serum creatinine (Cr) levels in the aged, we measured BUN and Cr levels in 332 cases of apparent-healthy elderly subjects (male, 152; female, 180) aged 70 years or more. We measured the variables also in 315 cases of sex-matched young control subjects (male, 139; female, 176). This study was a part of the Kahoku Longitudinal Aging Study (KLAS) that aims to reveal the comprehensive functions in the aged. We calculated the mean and the standard deviation (SD) in each group, and excluded subjects with values beyond twice the SD-line. We defined the normal range as range within the single SD-line of the remainder. The estimated normal range of BUN was 14-23 mg/dl both in male and female elderly subjects, and that of Cr was 0.9-1.3 mg/dl in male and was 0.7-1.1 mg/dl in female. The mean BUN level in the elderly subjects was significantly higher than that in the control young subjects. The mean Cr level in the elderly subjects was slightly higher than that in the control subjects. Significant positive correlation was found between BUN levels and age in male elderly subjects. Although Cr levels did not correlate with age in elderly subjects, Cr levels divided by body surface area significantly correlated with age. We concluded that the normal range of BUN and Cr levels differed between young and elderly subjects, and that the decline in renal function correlated with age after the seventh decade.