Critères d'évaluation de la validité d'un test biologique

Diagnostic tests are an essential part of clinical medicine, assisting the clinician in formulating diagnoses. Correct use of a diagnostic test requires to know its performance characteristics. Various indices are available to evaluate the test's validity and to help the clinician to choose the most suitable test. Sensitivity and specificity are important test features ; they measure the proportion of test-positive persons who truly are diseased and the proportion of test-negative persons who truly are non diseased. Predictive values provide an estimation of being sick or healthy according to the result of the test. They have the particularity of being sensitive to the prevalence of the disease and can rarely be generalised beyond the study. The likelihood ratio incorporates both the sensitivity and specificity of the test and provides a direct estimate of how much a test result will change the odds of having a disease. Their use in daily practice to calculate the post-test probability of the disease is facilitated by the use of Fagan's nomogram.