Ensuring correct interpretation of diagnostic test results.

Editor's Note Ensuring Correct Interpretation of Diagnostic Test Results Today, physicians order a wide array of diagnostic laboratory and imaging tests for their patients, including genetic evaluations.Tomakesenseof thegrowingnumberofdiagnostic testing opportunities, one might expect that physicians, in turn, have grown in their ability to accurately interpret test results. The Research Letter by Manrai and colleagues1 finds this not to be the case. They replicated a classic study and found that only 23% of physicians and physicians-in-training correctly answered a single questiontesting their interpretationofadiagnostic test result.While this study was limited to a convenience sample from a single academic teaching hospital, it is not too far out on a limb to suggest that today’s physicians need to be better prepared to interpret diagnostic test results, including stronger training in statistics and clinical epidemiology. In addition, this study reminds us that disease prevalence matters for testing, as does test accuracy (both sensitivity and specificity).However, these importantpiecesof informationare often lacking at the bedsidewhenwemake a decision to order atest.Generally,prevalenceisconsideredasonly“rare”or“common.” And howoften are physicians aware of diagnostic tests’ sensitivityandspecificity?Weneedresources thatmakethis informationmore easily and readily available. In themeantime,beforeorderinganytest,wemustaskourselves if it is even necessary. Assuming there are efficacious treatments for the disease being tested, what are our thresholds for “rulingout”diseaseon the lowendand“ruling in”disease on the high end of probability, and then, what is the pretest probability of the disease? If your pretest probability falls between those thresholds, is the test accurate enough that a positive or negative test finding will result in a posttest probability that crosses these thresholds? If the test result is not going to changeyour clinicalmanagement, there is no reason for the patient to undergo testing in the first place. The persistent inability of physicians to reliably manage this cognitive exercise implies that our educational programs need to do a better job at teaching numeracy skills. Because imprecise diagnostic decision making is leading to excessive testing,patientharm,andexcessivelycostlycare,wemust raise the bar andmaster these cognitive skills.