Biochemical values in persons older than 82 years of age: report from a population-based study of twins

According to international standards, reference values for biochemical tests should be obtained in disease-free subjects and for therapies that may influence measurement values. For elderly persons, especially the very old, such a requirement is difficult to meet, since few of these individuals are free of ongoing or former diseases. The present study of a population-based Swedish twin sample comprises 535 individuals (186 males, 349 females) who were at least 82 years of age at blood sampling. Survival over a 6-year period is used as a reference of overall health. Baseline test values for subjects surviving 6 years are compared with results for persons who died in the follow-up period. Results, including mean and median values, standard deviations and ranges, were given for both genders in the total sample. Cases outside the 5th and 95th percentiles were then excluded, as were those who died during the follow-up period. In a third step, cases with disorders and therapies known to influence measurement values were also excluded. The risk of dying during the observation period was calculated across measurements from the lowest and highest 10th and 20th percentiles. The specific impact of proximity to death on the biochemical values, in addition to age effects, was analysed by comparing co-twins discordant for survival over 7 years. Increased mortality was indicated for subjects of both genders with high serum levels of urea, urate, gamma-GT, free thyroxin and plasma homocysteine. In females, low serum values for albumin and total cholesterol were associated with increased mortality. A lower cholesterol level was found 4 years before death, while a lower HDL-cholesterol level was associated with an increased risk of death across the entire 7-year period.