AGE-RELATED-CHANGES IN LABORATORY TEST-RESULTS - CLINICAL IMPLICATIONS

Many quantities assayed in clinical laboratories demonstrate age-relat ed changes. Particularly important periods are early life, adolescence , old age, and after the menopause in females. The changes that occur until adulthood are well documented. Fewer data are available on elder ly people even though they consume a large component of healthcare res ources. In diagnosis, and prior to initiation of drug therapy, when no previous results are available, reference values must be available to aid interpretation. Reference intervals generated from elderly people are sometimes wider than in younger adults. It is suggested that conv entional adult reference values should be used in general for the very elderly since, at least in part, the wider intervals are probably due to inclusion of individuals who are unhealthy in the reference sample group. Most quantities have marked individuality, and serial values f or an individual span only a part of the reference interval. Individua ls can have values which are very unusual for them but still lie withi n the reference limits; this implies that clinical laboratory tests wi ll be less than ideal in the detection of latent or early disease. The average within-subject variation in healthy elderly people and younge r adults is similar. Therefore, the large database on biological varia tion can be used, with analytical imprecision, to calculate critical d ifferences for serial results in an elderly individual which must be e xceeded before significance can be claimed. These critical differences are of value in monitoring the effects of drug therapy.