Influence of index of individuality on false positives in repeated sampling from healthy individuals

Citation
Ph. Petersen et al., Influence of index of individuality on false positives in repeated sampling from healthy individuals, CLIN CH L M, 39(2), 2001, pp. 160-165
Citations number
7
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Medical Research Diagnosis & Treatment
Journal title
CLINICAL CHEMISTRY AND LABORATORY MEDICINE
ISSN journal
1434-6621 → ACNP
Volume
39
Issue
2
Year of publication
2001
Pages
160 - 165
Database
ISI
SICI code
1434-6621(200102)39:2<160:IOIOIO>2.0.ZU;2-J
Abstract
The index of individuality is defined as the ratio of the within-subject bi ological variation to the between-subject variation, i.e., the variation be tween the biological set-points. It has been disputed whether the index of individuality has influence on the usefulness of conventional population-ba sed reference intervals. In this investigation we found that, as long as on ly a single sample is taken, for a certain change in an individual's set-po int, the index of individuality has no influence on the usefulness of refer ence intervals. When two or more samples are taken into account, however, t he outcome of the measurement is highly dependent on the index of individua lity. For a low index, repeat measurement has only limited effect on the fr action of false-positive results, as the next result will be close to the f irst, but, when the index is high, the fraction of false-positive results w ill be reduced considerably through repeating the test. Moreover, the distr ibution of biological set-points for which the fraction of false-positive r esults originate is described and the influence of analytical imprecision i s discussed. The calculations are performed for values of the index of indi viduality from 0 to 2.0 for the traditional 95% reference interval based on (x) over bar +/- 2*s(total) (s(total) = total biological variation), and a lso for a decision limit (cut-off point) (x) over bar+/-3*s(total). The num bers are, of course, different, but the effects of the index of individuali ty are the same, independent of the chosen cut-off point. This concept is related to the clinical classification (diagnosis, prognosi s, screening) and the difference from different principles of monitoring is discussed. Further, five examples are evaluated and aspects of index of in dividuality in relation to false-positive results are discussed.