A Review of Molecular Diagnostic Tests

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What is a Molecular Test?

Molecular tests are a type of diagnostic (viral) test used for the detection of current COVID-19 infections among patients. Molecular tests utilize either reverse transcriptase-polymerase chain reaction (RT-PCR) or reverse transcriptase loop-mediated isothermal amplification (RT-LAMP) techniques, with the latter being quicker by not requiring thermal cycling need to amplify the viral RNA need for detection like RT-PCR does. Because RT-LAMP is quicker and   These both can detect the viral genetic material called RNA, as way to screen for the presence of the virus in a mucus sample collected from the respiratory tract [1].

How Many Different Molecular Tests Are Available and At What Cost?

There are currently over 200 different available molecular tests approved by the FDA via the Emergency Use Authorization, each offering a different level of accuracy and testing protocol [2]. Companies offer their tests at different prices, some as cheap as $20 per test, while others can cost up to $850[3]. Additional costs may incur from laboratory, hospital, and physician fees. However, these costs are not passed on to the patient and instead are covered through public health insurance such Medicaid and Medicare, as well as private health insurances. Federal law requires private insurers, Medicare, and Medicaid to cover the cost of a COVID-19 test without any cost to the patient through the Families First Coronavirus Response Act and the Coronavirus Aid, Relief, and Economic Security Act [4]. These acts also provide grants to the uninsured as a way to get tested for free. However, patients may be responsible to pay out of pocket fees if they choose to go to out-of-network providers.

Who Should Get Tested Using a Molecular Test? 

According to the World Health Organization, patients with clinical suspicion of a COVID-19 infection who receive an initial negative test result should retest, especially if symptoms are still present [5]. It is important to know that no molecular test result is definitive and social distancing guidelines should still be maintained. Caution should be taken when a patient is experiencing symptoms, even if an initial test result comes back negative. Although the molecular test is great tool utilized to detect active COVID-19 infections, they are not perfect and some incorrect results may be shared. It may be unclear if a symptomatic person tests negative because they may truly not have the disease or if they were given an incorrect result.

How Long Until Someone Can Get Their Results?

Samples are most often collected using a nasal or throat swab that is then sent to a laboratory where the sample is analyzed for viral presence. For the most part, laboratory testing can last several hours to weeks, depending on the capabilities and volume of tests received at the lab [6]. This may be unsuitable for someone who is in need of a fast test result or for an individual who is infected. Days might pass while the individual inadvertently infects others in their community while they wait for their test results to come back.

How Fast are Tests Able to be Analyzed and Where Can They be Performed?

Unfortunately, most RT-PCR molecular tests are limited by the large special equipment needed to analyze the samples as well as the longer time needed to run the analysis, making them inappropriate as a point of care test. However, there are few RT-LAMP tests available that can provide results in 15-60 minutes, making these more appropriate for point of care [7]. Although most of the molecular tests are unable analyzed in a point of care setting, they can be offered in a variety of settings, as long as the collected sample is sent to a laboratory for analysis. The samples can either be collected by lab personnel or even be sent through the postal services like LabCorp’s Pixel At-Home Collection Kit. Pixel provides a self-testing kit that can be done in the comfort of one’s own home that is sent back to the lab via FedEx, with results being provided 1-2 days after the samples are received [8]. The accuracy of these tests come into question when there is no supervision and self-administration is required. However, this test would not be utilized for someone in a skilled nursing facility.

What Do Test Results Mean?  

A diagnostic test can show if a patient or staff member has an active coronavirus infection and should take steps to quarantine or isolate themselves from others. The molecular tests detect the virus’s genetic material present in a mucus sample collected from an individual, in order to determine whether one has an active infection. 

How Accurate is the Molecular Test?

The molecular test is considered to be the gold standard diagnostic test utilized to COVD-19 infections that offers a high level of specificity and sensitivity. Specificity demonstrates how accurately a test can rule out patients who do not have the disease (true negatives) while sensitivity demonstrates how accurately a test can detect someone who has the disease (true positives).  However, the accuracy of molecular tests can vary depending on what product test is being utilized, with many of the tests providing different levels of accuracy. Ultimately, the best test to choose would ideally be one that includes the highest level of sensitive and specificity, as well as one that is easy to use and not require additional large expensive equipment to analyze a sample.

Other factors that can affect the accuracy of the test and potentially lead to a false negative include: improper handling and storage of both the samples collected and testing agents utilized in the analysis, inadequate sample collection, time from collection to the analysis of the test, current comorbid conditions, current medications, and testing too early. Sharing a false negative result with a patient may provide a false sense of security that can have detrimental effects on the larger community if the patient is not isolated from others. 

When Should Someone Get Tested?

 The timing of the test is another crucial aspect in determining the accuracy of a test. Testing too early may not provide ample time for a patient to develop a viral load large enough to be detected by the diagnostic test. Testing too late may also be problematic since antibodies can begin to remove the virus from the body, again decreasing the viral load to undetectable levels. The most accurate test results are obtained starting on Day 5 of the onset of infection through Day 14, with accuracy decreasing as the days go by [9].

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Prepared in collaboration with graduate students from Keck Graduate Institute (Claremont,CA): Srbuhi Poghosyan, Diego Salinas, Larisa Malak Stepanian, Michael Thompson

References

  1. https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics,accessed December 2, 2020

  2. https://www.fda.gov/medical-devices/coronavirus-disease-2019-covid-19-emergency-use-authorizations-medical-devices/vitro-diagnostics-euas,accessed December 2, 2020

  3. Peterson-KFF Health System Tracker. “COVID-19 Test Prices and Payment Policy.” https://www.healthsystemtracker.org/brief/covid-19-test-prices-and-payment-policy/, Accessed December 2, 2020.

  4. Health (ASH), Assistant Secretary for. “Community-Based Testing Sites for COVID-19.” Text. HHS.gov, May 6, 2020. https://www.hhs.gov/coronavirus/community-based-testing-sites/index.html.

  5. Diagnostic testing for SARS-CoV-2 Interim Guidance, World Health Organization, Published 11 September 2020, https://www.who.int/publications/i/item/diagnostic-testing-for-sars-cov-2, Accessed December 2, 2020

  6. “A Closer Look at Coronavirus Disease 2019 (COVID-19) Diagnostic Testing,” 2020, 4.

  7. administrator, JHCHS website. “Molecular-Based Tests for COVID-19.” Johns Hopkins Center for Health Security. Accessed December 1, 2020. https://www.centerforhealthsecurity.org/resources/COVID-19/molecular-based-tests/.

  8. Pixel by LabCorp. “COVID-19 Test (At-Home Collection Kit),” March 24, 2020. https://www.pixel.labcorp.com/at-home-test-kits/covid-19-test-home-collection-kit.

  9. Kucirka, Lauren M., Stephen A. Lauer, Oliver Laeyendecker, Denali Boon, and Justin Lessler. “Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction–Based SARS-CoV-2 Tests by Time Since Exposure.” Annals of Internal Medicine. Accessed December 1, 2020. https://doi.org/10.7326/M20-1495.