A study investigating a new test for diagnosing acute myocardial infarction (AMI) has just been initiated. The sensitivity of the test is estimated at 75% and the specificity at 80%. The study enrolls 600 patients, of whom 200 are confirmed AMI cases as determined by the diagnostic gold standard. How many false negatives are to be expected in the study?

Question

A study investigating a new test for diagnosing acute myocardial infarction (AMI) has just been initiated.  The sensitivity of the test is estimated at 75% and the specificity at 80%.  The study enrolls 600 patients, of whom 200 are confirmed AMI cases as determined by the diagnostic gold standard.  How many false negatives are to be expected in the study?

Quizplus · Accepted Answer

11ec160b_3721_4043_9249_830bc4fbede2_MD0001_00 The sensitivity of a test determines how well the test categorizes patients who have the disease of interest. Tests with higher sensitivity have an increased probability of assigning a positive test result to those patients who truly have the disease; these are considered true positives (rightmost part of the curve). Conversely, patients who test negative even though they have the disease are considered false negatives (leftmost part of the curve). True positives (TP) and false negatives (FN) are complementary (ie, an increase in one parameter is exactly offset by a decrease in the other, such that the total is always equal to the number of confirmed patients). As such, the test sensitivity and number of patients with the disease can be used to calculate the number of each: In this case, the sensitivity of the test is 75% and the total number of patients with confirmed acute myocardial infarction is 200. Therefore, a test that is 75% sensitive will correctly classify 75% of the patients as positive (TP) and incorrectly classify 25% of the patients (1 − Sensitivity) as negative (FN). Using this information, the number of FN can be calculated as follows (alternate method): Educational objective: When undergoing diagnostic testing, patients with the disease can test positive (true positive, TP) or negative (false negative, FN). The sensitivity of a test determines the proportion of patients that are correctly classified:

A Study Investigating a New Test for Diagnosing Acute Myocardial