The mathematics of measurement: sensitivity, specificity and predictive value of available tests

The correct clinical interpretation of any laboratory marker requires a good knowledge of its positive and negative predictive values, which are calculated from the sensitivity and the specificity of the test and from the prevalence of the disease. This means that we need a good assay technique in the case of biochemical tests, and a well defined reference sample (control subjects), with the ability to distinguish between a diseased and a healthy subject. In the field of alcohol abuse markers, each of these notions presents some degree of difficulty. There is no perfect solution, and a compromise has to be agreed upon.