Likelihood Ratio: A Powerful Tool for Incorporating the Results of a Diagnostic Test Into Clinical Decisionmaking

Decisionmaking thresholds. The numbers assigned to test and treatment thresholds will vary from one clinical setting to another (ie, 1%, 5%, 10%, and so on for test threshold, 80%, 90%, 99%, and so on for treatment threshold). They may differ for different diseases, and will be influenced by the clinical experience of the practitioner and by patient preferences. These thresholds should be determined by the clinician before obtaining the diagnostic test result. If no test result results in a posttest probability that either mandates treatment, consideration of alternative diagnoses, or discharge home, then the test will not aid clinical decisionmaking.

Nomogram for interpreting diagnostic test results.

A LR of. I will convert a pretest probability in the 30% to 90% range (intermediate to high) to a posttest probability in the 13% to 50% range (low to intermediate).

A LR of 10 will convert a pretest probability in the 10% to 60% range (low to intermediate) to a posttest probability in the 50% to 95% range (moderate to high).