Interpreting and Understanding Test Results

Hello and welcome back to the Corner. In this issue, I would like to discuss factors that should be taken into account when interpreting lab test results.  As testing for COVID-19 has increased, and will likely continue into the future, this provides a great example of how to interpret and use testing results.

Often times there are many different types of tests that can be used to detect a condition, or past exposure to a condition. Currently for COVID-19, serology tests, molecular or PCR tests, and antigen testing are available.  While there may be some similarities in how the tests are administered or how samples are collected, they may differ in what the results mean.

At this time, there is no test that is 100% sensitive, specific, or predictive.

In order to accurately interpret the results, it is important to know both the sensitivity and specificity of the particular test.

The “sensitivity” of a test refers to how confident you can be in a negative result. 

In a highly-sensitive test, the results should provide less false-negative results, resulting in more confidence the patient truly does not have the condition. In contrast, the “specificity” of a test strengthens the confidence in a positive result.  In a highly-specific test, there is less chance of a false-positive result because the test is looking for a very particular, distinct character or trait.  Based on this, the best test would be one that exhibits not only a high-sensitivity, but also a high-specificity to rule out both false-positives and negatives.  Once the sensitivity and specificity of the test are determined, scientists can use predictive modeling to accurately interpret the results.

In the case of COVID-19 testing, positive and negative values can mean different things depending on the type of test that is being used.  For instance, in testing for active infections, a positive result indicates the patient most likely has the infection while a negative indicates they may not.  Other types of testing can show if the patient potentially had the infection in the past, never had it, or has even recovered from it.  Each test is unique regarding positive and negative results and what they mean compared to what the test was intended to identify. Again, all of the tests used have limitations based on the sensitivity and specificity and therefore could lead to false-positive or false-negative results.  This is why testing should be accompanied by other means to determine infections such as patient history, recent travel or exposure, and presence/absence of symptoms.  As we move into the future, the hope is not only that COVID-19 testing will become more sensitive and specific, but the same can be said for other laboratory tests.

Thanks again for stopping by and see you next month!