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Sharp Health News

Which COVID-19 test is best?

Jan. 13, 2022

COVID-19 swab test

COVID-19 testing experiences across the country have been varied. While one person may receive test results within minutes, another can wait more than a week to know whether or not they have been infected. Some people choose to pay hundreds of dollars out of pocket at a pop-up testing site, while others are able to secure free at-home testing kits at their local library.

Regardless of the amount you might pay for a test or the time it takes to receive your results, Dr. Omid Bakhtar, a board-certified pathologist affiliated with Sharp HealthCare, says testing plays a vital role in helping to stop the spread of COVID-19.

Types of COVID-19 diagnostic tests
There are currently two primary types of approved COVID-19 tests used to determine the presence of viral infection in both vaccinated and unvaccinated people:

  • Nuclear acid amplification tests (NAAT) — a common example is a PCR test — detect the virus’s genetic material. The sample is taken with a nasal or throat swab, or from a person’s saliva. The tests are highly accurate, but results can take up to 1 week. In fact, these tests are so incredibly sensitive that in some scenarios they may detect “genetic” fragments of a prior or waning infection, meaning the person whose sample was tested and is deemed positive may be carrying a very low viral load and is less likely to be contagious.
     
  • Antigen tests — sometimes referred to as rapid tests — detect specific proteins on the surface of the virus. The sample is taken with a nasal or throat swab either at a testing facility or using an FDA-approved at-home test, and results can be produced within minutes in some cases. While positive results are usually accurate, negative results may need to be confirmed with a PCR test. These tests perform best when the person is tested in the early stages of COVID-19 infection, when viral load is highest.

“While antigen tests are faster, less expensive and don’t require the level of laboratory equipment that PCR tests do, they are specifically made to be used in people who have symptoms,” Dr. Bakhtar says. “They also have a higher likelihood of producing false-negative results.”

However, Dr. Bakhtar reports that antigen tests are highly accurate in determining positive results and are valuable when used to perform screening within large populations, such as school students or employees of large companies. This type of screening must be done repeatedly to quickly identify people with active COVID-19 infection and to accumulate data on the rate of infection within a population.

“Similarly, antigen tests can also be used in asymptomatic people who have had a COVID exposure,” he says. “In such scenarios, they are best used in a repeated fashion, such as performing two to three tests, two days apart.”

Another type of testing, antibody testing — also known as serology testing — screens for past infection or prior vaccination. The test determines the presence of antibodies — nucleocapsid antibodies from past infection or spike antibodies from prior vaccination — which are proteins that fight off infections and can often provide immunity against catching the same infection again.

However, most currently available antibody tests do not screen for active COVID-19 infection and cannot be used for diagnostic purposes. Moreover, the utility of antibody testing for vaccination status is not well established and is currently not recommended.

When to be tested and what to do with the result
The CDC recommends people should be tested for COVID-19 if they:

  • Have symptoms of COVID-19, regardless of vaccination status
  • Are unvaccinated and had close contact — were within 6 feet of an infected person for a total of 15 minutes or more — with someone who is confirmed to have COVID-19, regardless of whether experiencing symptoms or not
  • Are vaccinated and had close contact with someone who is confirmed to have COVID-19 and are experiencing symptoms
  • Have been asked or referred to get testing by their health care provider or the health department

Once tested, people should quarantine at home until they receive their test results.

If you test positive, you can assume you have COVID-19 and are contagious. You should follow all isolation and prevention guidance to protect others from getting sick.

In California, this includes staying home for at least 5 days. Your isolation can end after day 5 if you do not have symptoms and test negative on day 5 or later. However, you should continue to wear a well-fitting mask around others for a total of 10 days, especially in indoor settings.

In all other cases, the isolation guidance is:

  • If you are unable to test or choose not to test, and you do not have symptoms or your symptoms are resolving, your isolation can end after day 10.
  • If you have a fever, your isolation should be continued until your fever resolves without the use of fever-reducing medication.
  • If your symptoms other than fever are not resolving, you should continue to isolate until all symptoms are resolved or until after day 10.

If you test negative, it means that you probably did not have COVID-19 at the precise moment your sample was collected. However, it is important to remember the risk of false-negative results if a rapid antigen test was performed.

According to Dr. Bakhtar, a follow-up PCR test may be in order, especially if you have been exposed to COVID-19 or are experiencing symptoms. Until that test can be performed, you should continue to follow prevention guidance.

How to get tested
San Diego emergency rooms and urgent care centers are currently experiencing high volumes of patients. If you need a COVID-19 test, it is recommended you go to a designated testing location, rather than an ER or urgent care, unless you have significant COVID-19 symptoms and are at risk for serious illness.

Local health experts recommend the following testing resources:

  • If you have severe illness — or are at risk for severe illness — contact your health care provider.
  • If you need to be tested due to a confirmed exposure or you are experiencing symptoms and are under age 65 with no underlying health conditions, you can visit one of the options offered by San Diego community and health care partners. You can also purchase self-test kits at some local pharmacies or online. Some public health agencies and school districts are providing free at-home kits as supplies allow.
  • If you do not have COVID symptoms, have not had an exposure, or are under age 65 with no underlying health issues, but need to be tested for school, travel, work or for other purposes, visit a County of San Diego testing location or consult your school, employer or travel company for testing options.

“Knowing whether you have COVID-19 is a ‘here and now’ situation, as a test today can’t tell whether you might have it two, five or 10 days from now,” Dr. Bakhtar says. “Regardless of your vaccination status, if you are experiencing symptoms, you should get tested and could consider testing again five days later.”

Learn about COVID-19 screening and testing at Sharp.

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