Biostatistics Advance Access originally published online on June 19, 2006
Biostatistics 2007 8(2):285-296; doi:10.1093/biostatistics/kxl009
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Bayesian detection of abnormal values in longitudinal biomarkers with an application to T/E ratio
Swiss Laboratory for Doping Analyses, Université de Lausanne, 1066 Lausanne, Switzerland. Chemin des Croisettes 22, 1066 Lausanne, Switzerland pierre-edouard.sottas{at}hospvd.ch
Swiss Laboratory for Doping Analyses, Université de Lausanne, 1066 Lausanne, Switzerland
Swiss Federal Office for Sports BASPO, 2532 Macolin, Switzerland
Swiss Laboratory for Doping Analyses, Université de Lausanne, 1066 Lausanne, Switzerland
* To whom correspondence should be addressed.
We developed a test that compares sequential measurements of a biomarker against previous readings performed on the same individual. A probability mass function expresses prior information on interindividual variations of intraindividual parameters. Then, the model progressively integrates new readings to more accurately quantify the characteristics of the individual. This Bayesian framework generalizes the two main approaches currently used in forensic toxicology for the detection of abnormal values of a biomarker. The specificity is independent of the number n of previous test results, with a model that gradually evolves from population-derived limits when n = 0 to individual-based cutoff thresholds when n is large. We applied this model to detect abnormal values in an athlete's steroid profile characterized by the testosterone over epitestosterone (T/E) marker. A cross-validation procedure was used for the estimation of prior densities as well as model validation. The heightened sensitivity/specificity relation obtained on a large data set shows that longitudinal monitoring of an athlete's steroid profile may be used efficiently to detect the abuse of testosterone and its precursors in sports. Mild assumptions make the model interesting for other areas of forensic toxicology.
Keywords: Bayesian statistics; Biomarker; Doping; Longitudinal study; Steroids
Received March 24, 2006; revised May 24, 2006; accepted for publication June 8, 2006.
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