November 10, 2020
As the winter flu season approaches, COVID-19 management and testing become essential as it is difficult to differentiate the respiratory diseases caused by these viral pathogens. Here we intend to provide information about COVID-19 testing options which could be used as a quick reference. The information from this article is in line with CDC guidelines.
To diagnose a current infection:
PCR Test (Polymerase Chain Reaction): this is a molecular test looking for genetic material that comes only from the virus. The test is commonly conducted at a certified laboratory and takes a few hours to complete. Thus, it is common that the result is reported in 1-3 days. The specimen for this test is collected via nasal swab.
Currently, this is the most accurate test to diagnose an active COVID-19 infection. Patients who receive a positive test result are contagious and can transmit the virus to others through close contact.
This test can be used by a symptomatic person for diagnostic purposes, or by an asymptomatic person needing a negative result for work, school, or travel. It can also be used for anyone suspected of high-risk exposure to the virus. However, this test could result in a false negative reading, which can result in misdiagnosis of someone who is infected. The error is largely due to the incorrect collection of nasal swabs.
Rapid test: This is an antigen test, designed to detect viral protein (called antigens) on the surface of the virus. This test can be done in a physician’s office or hospital via nasal or throat swab. The result is available in 15-20 minutes.
A rapid (antigen) test is ideal for a symptomatic person or in a highly-infectious area for the purpose of identifying positive infections so social isolation can begin sooner rather than later. It can also be used repeatedly due to the convenience and quick turnaround of results.
However, a negative rapid test result should be treated as presumptive, as the test is not as sensitive as a PCR test. With this consideration, it does not rule out a COVID-19 infection and should not be used as the sole basis for treatment or patient management decisions. If a patient is symptomatic or has had high-risk exposure but tested negative in the rapid test, it is recommended that the patient follow up with a PCR test.
To diagnose a prior infection:
Antibody tests can determine if the person has the history of the virus infection, but it does not necessarily indicate an active infection. There are two types of antibodies in humans responding to the virus: IgG, which commonly appears approximately 14 days after a viral infection and persists for life; and IgM, which appears early after infection and disappears after a couple of months. This test is performed by collecting a blood sample.
All healthy individuals will develop antibodies following a COVID-19 infection. IgG is a reliable marker for the viral infection, but it does not indicate when the patient had the virus. IgM is less reliable in assays, but could indicate a recent infection, potentially suggesting that the patient is contagious with an active infection. However, IgM assays are typically come with a high rate of false negative results.
The antibody test is useful to understand the past history of infection.
Both are upper respiratory diseases that share similar symptoms: chills or fever, fatigue, cough, and sore threat. It is important to get a flu shot to prevent the flu and continue to follow CDC guidelines to reduce your risk of exposure to COVID-19, including wearing mask and practicing social distancing.
• Seek medical care immediately via telehealth or an in-office visit.
• Get a coronavirus test as soon as possible, preferably a PCR test.
• Stay home until a coronavirus test is confirmed negative and your symptoms subside.
• If you test positive, stay quarantined until confirmation of a negative result from a repeat test two weeks post initial infection.
As always, we urge everyone to please closely follow CDC guidelines: wearing a mask, practicing social distancing, and getting a COVID-19 test if you experience symptoms or have high-risk exposure to the virus. Please remember your flu shot this fall to avoid this vaccine-preventable disease.