Requirements and assessment of laboratory tests: Part 5 of a series on evaluation of scientific publications.

BACKGROUND

Current laboratory tests exhibit high sensitivity and specificity combined with comparatively low costs thus favoring broad and uncritical ordering habits.

METHODS

Introduction of Bayes' theorem and discussion of its implications for laboratory test results in a mostly non-technical form, accompanied by a selective literature review.

RESULTS AND CONCLUSIONS

According to Bayes' theorem the positive predictive value of laboratory test results is directly dependent on the prevalence of the disease in a given patient cohort. Thus, the clinical value of a given test result is critically dependent on a precise indication. Ordering of tests that are not indicated in a given patient is clinically useless and undesirable, where detailed information on disease prevalence is missing. These considerations are valid irrespective of ethical or economic considerations.