COVID-19 Testing – SnNOout vs. SpPIn, What Does it Mean?

As a pharmacist’s role within the COVID-19 pandemic expands, pharmacists need to have the capability to administer COVID-19 tests and communicate the results to patients. Pharmacists need to evaluate a test to ensure patients receive all pertinent information on their results. Sensitivity and specificity are two ways to evaluate a laboratory test and describes how often the test is right.

Sensitivity describes the true positive (TP), or the probability of a positive test result. Specificity describes the true negative (TN), or the probability of a negative test result. There are two acronyms to assist with remembering this concept, SnNOut and SpPIn. SnNOut refers to a highly Sensitive test, if Negative, rules Out the condition. SpPIn refers to a highly Specific test, if Positive, rules In the condition. The importance lies in that not all tests are 100% accurate.  Pharmacists should investigate the sensitivity and specificity of available tests and include those factors when selecting the test to offer. Therefore, by reading and understanding the “performance characteristics” of test package labels, pharmacists can communicate the probability that a test result can be trusted.

The following chart will be used to walk through an example. For instance, the Cellex qSARS-CoV-2 IgG/IgM Rapid Test is 93.8% sensitive and 95.6% specific. If 200 patients are tested using this method and 100 receive positive test results, then 93-94 patients will have a positive test result and have COVID-19 (A) and 6 to 7 patients will have a positive test result and not have COVID-19 (C). Furthermore, 100 patients receive a negative test result. Of those 100 patients, 95 to 96 patients will have a negative test result and not have COVID-19 (D) and 4 to 5 patients will have a negative test result but have COVID-19(B).

Sensitivity and specificity

The key takeaway is that even though a patient may receive a negative test result, this does not preclude the patient from having the disease and vice versa. Therefore, always check a test’s “performance characteristics” to be able to guide a patient through understanding their results and interpreting their meaning.

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Posted July 2020

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