In a recent webinar from TRC Healthcare Healthcare’s Emerging Recommendations Panel on July 16, 2020, an expert panel discussed COVID-19 types of tests and caveats. The panel consisted of Lori Dickerson, Pharm.D., FCCP as the moderator, joined by Reid Blackwelder, M.D., FAAFP, Jehan Budak, M.D., Steven Nissen, M.D., MACC and Craig Williams, Pharm.D., FNLA, BCPS. They noted that pharmacists are getting more involved with testing as pharmacists in every state are authorized to order and administer SAR-COV-2 testing.
The first set of tests is the diagnostic tests. These tests use swabs to obtain specimen from the nasopharyngeal, nasal or oropharyngeal cavity. One type of most common diagnostic tests is polymerase chain reaction (PCR) testing. PCR is a molecular test that detects viral RNA presence in a sample. Most tests must show a 95 percent sensitivity and 100 percent specificity in order to be eligible for the emergency use authorization (EUA). Although during some cross studies, some tests were shown to be only 79 percent sensitive but results may have been from faults with the transport media being utilized. Point of care (POC) antigen testing is another diagnostic test that tends to have a turnaround time under 30 minutes verses hours for a PCR test. While being faster to generate an answer, they tend to only be 80 percent sensitive. PCR testing is more accurate, but POC antigen testing provides quicker results. Some institutions are screening with the antigen testing and confirming negative tests with PCR in order to rule out false negatives. For patients who test negative in the community but are still experiencing symptoms, TRC Healthcare recommended retesting immediately if an antigen test was used originally or to retest two-three days after a molecular test. Dr. Budak recommended utilizing molecular testing as the preferred retest if at all possible.
The sample collection can also lead to false negatives as the different tests can be difficult to perform. Nasopharyngeal is preferred, but harder to collect. Dr. Budak’s practice considers oropharyngeal the lowest tier sample to collect. Sputum tests in the pipeline were mentioned. This expert panel acknowledged that many physicians and pharmacists are not always able to pick which test their facility is utilizing, but recommends any test over not testing.. It is also worth noting that the tests can return a false negative if swabbed too early in the viral process where the viral load is too low as the nasal viral load can vary for each individual.
They recommended against re-testing a patient who had previously tested positive for SARS-COV-2 to see if the virus has cleared. This is because the dead virus may still be present in the nares for some time after the infection has completed. Consistent with the Centers for Disease Control and Prevention, TRC Healthcare recommended and the panel agreed that isolation can end after 10 days of symptom onset if symptom free for at least 72 hours.
The other type of testing is the antibody test to determine if someone had a previous infection. It is collected by blood sample or venipuncture. Obtaining a EUA from the Food and Drug Administration for antibody testing assumes 90 percent sensitivity and 95 percent specificity. A negative test indicates that a patient likely did not have COVID-19. The positive test from antibody testing cannot guarantee that a patient had COVID-19 specifically is exposure is uncertain due to false positives. When disease presence is low, the chance for false positives is high. There is not currently an area in the U.S. where the disease is common enough to make the positive predictive value much over 50 percent. With this, patients are cautioned against assuming immunity due to a presumed true positive test.