COVID-19 was declared a pandemic in March 2020 by the World Health Organization, considering that it had spread to various countries across the world. Little was known about this disease which first made headlines in December 2019 when discovered in Wuhan, China. The lack of information regarding its mode of transmission at the time meant that there were no elaborate diagnostic screening methods. Fast forward, scientists have made big breaks in that there is much information on the disease thanks to numerous research studies. Today, several FDA-approved diagnostic screening tests are used on both symptomatic and asymptomatic individuals either in the laboratory or at home. They are classified as either antigen, molecular, or antibody tests for diagnosing current, past, or suspected infections. A comparison of polymerase chain reaction (PCR) and rapid diagnostic test (RDT), which are some of the FDA-approved COVID-19 screening methods, will form the basis of this discussion.
Polymerase Chain Reaction (PCR) Test
The test, also known as molecular testing, is used to detect the virus’ genetic material using polymerase chain reaction (PCR), a lab technique. During this procedure, the physician will insert a long swab into the back of a patient’s nose to collect fluid samples. At the same time, the physician may use a shorter swab to collect nasal fluid for testing. In other cases, a long swab may be inserted at the back of a patient’s throat to get a saliva sample, or the patient is required to spit on the swab (Bisoffi et al., 2020). Once the physician has gotten the sample, it is analyzed onsite or using the extraction process to isolate genetic materials associated with the virus causing COVID-19. The testing process relies on a PCR machine known as a thermal cycler, and special chemicals react to produce millions of the SARS-CoV-2 virus’s genetic material. Patients’ results may take a few days in case of a surge in laboratory requests.
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PCR testing is not limited to any age group considering that it uses swabs to collect samples from the nasal cavity, throat, or mouth. PCR tests are used on individuals from any age group suspected of having COVID-19 even if they do not show any symptoms. PCR testing is recommended for children, and it is viewed as the gold standard for determining if they have an active infection (American Academy of Pediatrics, 2021). The PCR test results are used to establish the presence of SARS-CoV-2 RNA, which is detectable in patients in the acute phase of infection. Positive results show a higher likelihood of being infected with the virus, but there is a need to correlate diagnostic information and history to determine the infection status. Most individuals with a positive result may be having a mild illness, meaning that they may not need medical attention as they may recover safely at home. On the other hand, adverse results should not be used as a basis for making decisions on patient management since they do not preclude SARS-CoV-2 infection (George et al., 2020). A negative result indicates that at the time of the test, the individual may be infected, but the virus is not enough to be detected using the PCR test.
Rapid Diagnostic Test
This screening method classified under serology antibody testing is used to detect the immunoglobulins produced by plasma B cells on exposure to foreign antigens. RDT is considered a rapid and simple test aligned with the lateral flow immunoassay (LFIA) technology which is also evident in pregnancy test kits (Peeling et al., 2020). Its simplicity means that it has the potential for being administered at the point of care as well as for self-testing. RDT test, unlike the PCR, uses a drop of blood in detecting if there are antibodies that have been released against specific SARS-CoV-2 antigen. According to Ghaffari et al. (2020), the RDT test is one of the easiest forms of testing as the patients get their results within 10 to 30 minutes. In this case, it may be deployed to conduct large-scale serological testing to contain the spread of the virus. Therefore, it has the potential to be deployed in large-scale serological surveys. Rapid diagnostic tests may be used on individuals from all age groups, although their effectiveness is dependent on various factors. Ghaffari et al. (2020) note that the antibody response's strength depends on patients’ nutritional status, age, the severity of the disease, and certain infections or medications. In this case, it means that RDT is more effective during the recovery stage as the patient will have developed the antibodies.
Predictive Ability of PCR and RDT Rests
PCR test has been proven to be very reliable in identifying active infections, most notably SARS-CoV-2. PCR achieves high levels of specificity and sensitivity, meaning that their reliability reduces the likelihood of misdiagnosis. In a study conducted by George et al. (2020), the PCR test using nasopharyngeal swab had 87% sensitivity and 97% specificity with a positive predictive value of 0.98, while its negative predictive value was 0.80 in symptomatic patients. On the other hand, RDT tests are preferred since they produce test results quickly. However, they are less reliable when compared with PCR, considering that they have good specificity but moderate sensitivity. According to Bisoffi et al. (2020), the WHO recommends a minimum of 97% specificity and 80% sensitivity for RDTs for patients with consistent symptoms with COVID-19. However, the VivaDiag IgM (RDT) indicated 98.5% specificity and a positive predictive value of 84.0% PPV, but 24.7% sensitivity (Bisoffi et al., 2020). These figures indicate that molecular tests, especially PCR have more clinical utility as compared to serological tests.
Integrating PCR and RDTs into Advanced Clinical Practice
PCR and RDTs are crucial diagnostic tools in assessing if patients are infected with COVID-19 or not. The reason that I would use PCR is the fact that it is very accurate and reliable in establishing if patients have the virus RNA or not. In the same way, I would integrate RDT, especially when conducting large-scale serological tests, since it provides immediate feedback. However, I would be hesitant to use RDT as it has a low sensitivity meaning that it is only accurate during the recovery phase when it is too late to intervene. To this end, I would integrate both but use PCR more because of its overall sensitivity and specificity.
References
American Academy of Pediatrics. (2021). COVID-19 testing guidance . https://services.aap.org/en/pages/2019-novel-coronavirus-covid-19-infections/clinical-guidance/covid-19-testing-guidance/
Bisoffi, Z., Pomari, E., Deiana, M., Piubelli, C., Ronzoni, N., Beltrame, A., Bertoli, G., Riccardi, N., Perandin, F., Formenti, F., Gobbi, F., Buonfrate, D., & Silva, R. (2020). Sensitivity, specificity and predictive values of molecular and serological tests for COVID-19: A longitudinal study in emergency room. Diagnostics,10 (9), 669-681. https://doi.org/10.3390/diagnostics10090669
George, B., McGee, J., Giangrasso, E., Finkelstein, S., Wu, S., & Glatt, A. E. (2020). What is the predictive value of a single nasopharyngeal SARS-CoV-2 PCR swab test in a patient with COVID-like symptoms and/or significant COVID-19 exposure? Open Forum Infectious Diseases , 7(10), 34-52. https://doi.org/10.1093/ofid/ofaa399
Ghaffari, A., Meurant, R., & Ardakani, A. (2020). COVID-19 Serological tests: How well do they perform ? Diagnostics, 10 (7), 453-462. https://doi.org/10.3390/diagnostics10070453
Peeling, R. W., Wedderburn, C. J., Garcia, P. J., Boeras, D., Fongwen, N., Nkengasong, J., Sall, A., Tanuri, A.,& Heymann, D. L. (2020). Serology testing in the COVID-19 pandemic response. The Lancet, 20(9), 245-249. DOI:https://doi.org/10.1016/S1473-3099(20)30517-X
