As the COVID-19 pandemic continues to spread across the country, many nurse practitioners (NPs) and physician assistants (PAs) are receiving mixed information about who should be tested and when testing should occur. The Clinical Advisor spoke with Jonathan Ives, PA-C, a pulmonary/critical care PA from Texas Pulmonary and Critical Care in Fort Worth, Texas, about when to test, how to test, and how to interpret the test results.
Q: On May 3, 2020, the Centers for Disease Control and Prevention revised their criteria for who should be tested. What advice would you give NPs/PAs about the status of the current testing for SARS-CoV-2 virus?
A: In the beginning, the CDC criteria for COVID-19 testing was very strict. We are no longer just testing patients that have had contact with a patient with a confirmed infection.
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Currently, the community prevalence of COVID-19 is such that we cannot rule out the potential of infection too quickly; we may end up having to test patients when there is a high level of suspicion based on their symptoms, medical history, etc. We also have to think about COVID in patients with co-infections; just because a person has pneumococcal pneumonia does not mean that they don’t also have COVID-19, for example.
The bottom line is to be extra cautious. Once we start to move patients out of isolation and let them circulate with staff, we are going to see a large spike in nosocomial infections, and then a large surge in our communities.
Q: How accurate are the current tests?
A: There are new studies coming out in the literature about the accuracy of the COVID-19 tests: what is their specificity and what is their clinical role. The most commonly used test to diagnose COVID-19 is the RT-PCR test.
A PCR test is a molecular assay that requires a highly functioning laboratory. Since the coronavirus is an RNA virus, a sample swab, either a nasopharyngeal or oropharyngeal, must be sent to a laboratory to go through several steps to convert the RNA into viral DNA— that is the reverse transcription (RT) part of the RT-PCR.
Then the PCR test takes a small amount of DNA and amplifies specific sequences of the genetic material to diagnose an acute infection. The key point here is that the RT-PCR test is looking for acute infection, not whether the patient has recovered from COVID-19. The test is very specific for the virus. If a patient tests positive, it’s very likely that the patient has COVID-19. However, this high specificity comes with a trade-off in terms of sensitivity. For example, the further out in time from when the patient had symptoms and is tested, the more likely the test will be false-negative, or perhaps may no longer be infectious. If a patient is >10 days since they have had symptoms, the false-negative rate goes way up.
The accuracy of the test can also depend on where the sample is taken—whether it is from the naospharynx or oropharynx cavity—the deep nasopharynx swap appears to be the best location.
Q: Is there a lot of variation in the accuracy of test results based on laboratories?
A: No. The various laboratories are using the same technology and fundamental building block of DNA testing. The sensitivity and specificity numbers are going to vary depending on when a patient is tested and the type of the sample taken. Generally, the specificity of the tests are in the high 90%. But the sensitivity of testing really varies a lot. In my facility, the sensitivity is around 70%, but that’s just a generic blanket number that really doesn’t encapsulate the illness and when a patient is going to have the RNA of the virus in their throat.
