Which value is calculated using the total number of normal noninvasive tests as its denominator?

The correct choice relates to the concept of Negative Predictive Value (NPV). NPV is calculated using the total number of true negative results (those tests correctly identified as negative) divided by the total number of noninvasive tests that yielded a negative result. In this context, the denominator consists entirely of the normal noninvasive tests, which allows for a direct assessment of how well the testing method rules out disease when the results are negative.

Specificity and sensitivity, on the other hand, focus on correctly identifying true positives and true negatives relative to total positives or total tests, but they do not specifically use just the total number of normal tests in their calculations. Positive predictive value relates to the accuracy of positive test outcomes but is based on the number of tests that resulted in a positive diagnosis. Thus, the unique focus of NPV on the total number of normal noninvasive tests clarifies why it is the correct answer.