A recent study investigated whether the ratio of peak tricuspidregurgitant veloc
ID: 2950692 • Letter: A
Question
A recent study investigated whether the ratio of peak tricuspidregurgitant velocity (TRY, ms) to the right ventricular outflowtract time-velocity integral (TVI, cm) obtained by Dopplerechocardiography (TRV/TVI) provides a clinically reliable method todetermine pulmonary vascular resistance (PVR). PVR is a variable inmanagement of patients with pulmonary and cardiovasculardiseases.
A sensitivity of 77% and a specificity of 81% were found indetermining if the patient had a high PVR. This was found using aspecific TRV/TVlRvox value as a cut off between high and low PVR.Assume that the prevalence of a high PVR in cardiac patients is 45per 100.
a) If the test result indicates ahigh PVR value, what is the probability the person
actually has high PVR? In other words, what is the predictive valueof a positive test
result for this test?
b) What is the probability of a false negative result usingthis test?
Explanation / Answer
Sensitivity measures the proportion of actual positives that arecorrectly identified. Specificity measures the proportion ofnegatives that are correctly identified. Sensitivity = (true positives) / (true positives + false negatives)= 77% Specificity = (true negatives) / (true negatives + false negatives)= 81% a) The predictive value of a positive test result is true 77% ofthe time. b) The probability of a false negative is 1 - 81% = 19%.