Sensitivity of a Test

Sensitivity is the proportion of true positive tests out of all patients with a condition.

In other words, it is the ability of a test or instrument to yield a positive result for a subject that has that disease. A test that is 100% sensitive means all sick individuals are correctly identified as sick, i.e., there are no false negatives. Importantly, as the calculation involves all patients with the disease, it is not affected by the prevalence of the disease.

The ability to correctly classify a test is essential, and the equation for sensitivity is the following:

Figure: Deriving the Formula for Sensitivity

Sensitivity does not allow providers to understand individuals who tested positive but did not have the disease.

A good diagnostic test should be sensitive as well as specific for detection of a health condition or disease.

Resources

• Diagnostic Testing Accuracy: Sensitivity, Specificity, Predictive Values and Likelihood Ratios; Jan 2021, Jacob Shreffler; Martin R. Huecker.
• Sensitivity and Specificity Explained: A Cochrane UK Trainees Blog.

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