What Type of Diagnostic COVID Test to Take and When

woman having her nose swabbed for COVID-19 test

COVID-19, the disease caused by infection with the novel coronavirus, continues to sicken people around the world. COVID-19 testing is now available in most places, but it can be difficult to know when to seek testing. Symptoms of COVID-19, including cough, congestion, fever, diarrhea and fatigue are vague and not specific for COVID-19. And some infected individuals never develop noticeable symptoms.

Understanding the current recommendations for when to take a COVID test after exposure (and when to retest) can help you make informed, responsible healthcare decisions.

Types of Diagnostic COVID Tests

At present, there are two primary types of COVID tests on the market to diagnose an active infection:

Molecular tests

These tests detect a bit of the genetic code of the virus. Molecular COVID-19 tests are sometimes called PCR tests; PCR stands for polymerase chain reaction, which is the chemical technique these tests use to spot the virus. These tests may also be called nucleic acid amplification tests.

Molecular tests are highly sensitive and almost 100% accurate in detecting COVID-19 infection. However, it typically takes a while to get results—usually, at least a day; sometimes, longer.

Keep in mind that SARS-CoV-2, the virus that causes COVID-19, has a 2- to 14-day incubation period. If infected, it could be up to 14 days after exposure before you test positive, even if you don’t experience symptoms. (The typical time is 5 days.) In general, molecular tests are most reliable 1 to 2 days before symptoms appear and up to several weeks after.

Antigen tests

These tests detect proteins on the surface of the virus. Antigen tests return results quickly—often, in less than 30 minutes. However, these tests are not quite as sensitive as PCR tests. They also have a narrower window of accuracy after exposure. According to the CDC, “positive results from antigen tests are highly accurate, but there is a higher chance of false negatives.” A false negative is a negative test result when the person is actually infected with the virus.

Scientific studies have shown that antigen tests are most reliable when taken within a week of developing symptoms. An infected person who has an antigen test too early (before symptoms) or too late (after symptoms) may get a false negative result.

At-home COVID tests

The first at-home, rapid antigen COVID test available without a prescription was recently approved by the FDA (U.S. Food and Drug Administration). Prior to its approval, there were several at-home COVID-19 diagnostic tests. However, most of the "tests" are actually sample collection kits available for purchase online or at stores like Costco; individuals either swab their nose as directed or spit into a tube and send the collection kit back to a lab for PCR analysis. Test results come back a day or two after the lab receives the sample.

The FDA has approved many other rapid antigen tests, typically administered by healthcare professionals. But, the recently approved test is the first one available over the counter without a doctor"s prescription. There will be a very limited supply until manufacturing ramps up. The FDA is approving more rapid diagnostic tests for home use, but some of these will require a healthcare provider"s prescription.

When to Take a COVID Test

The U.S. Centers for Disease Control and Prevention (CDC) recommends COVID-19 testing for active coronavirus infection if:

  • You have symptoms of COVID-19, including fever, cough, congestion, loss of taste of smell, fatigue, headaches, muscle aches, diarrhea, or shortness of breath. Don’t assume you have a cold, allergies, sinus infection, or “the stomach flu.” The molecular test is the gold standard for COVID-19 diagnosis. A rapid COVID antigen test may be suitable for quick results, but a provider would most likely want to confirm the positive result with a molecular test.
  • You have been in close contact with someone who tested positive for COVID-19. The CDC defines “close contact” as spending a total of 15 minutes or more within 6 feet of someone. There is no set number of days after close contact to be tested, but a general guideline is not to test in the days immediately following exposure. The molecular test is most sensitive; however, you could test negative with the molecular or antigen test and still test positive a day or two later. See below, When to Take a 2nd COVID Test.

Your healthcare provider may also recommend COVID-19 testing if:

  • You have been in close contact with someone who likely has COVID-19. Some individuals choose to not test themselves for COVID-19. If you’ve recently spent time with someone who has since developed COVID symptoms, consider testing. Ask your provider or your local public health department about your testing options.
  • You recently attended a gathering of 10 or more people in an area that currently has high levels of COVID-19 infection, especially if all attendees did not wear masks and maintain 6 feet of social distance from one another. Individuals can be infected and spread the virus even if they don’t have any symptoms. Follow the same guidance as for close contact with someone who likely has COVID-19.

When to Take a 2nd COVID Test

Because antigen tests can give false negative results, healthcare providers and public health officials recommend a 2nd COVID test via molecular testing for anyone who has symptoms of COVID-19 but received a negative antigen test result. An individual who was likely exposed to COVID-19 but tested negative via an antigen test should also consider a 2nd COVID test.

Remember it could be 14 days from the time of exposure before you have detectable virus levels and a positive test result. The median is five days. It is best to quarantine for 14 days, if possible, pending test results, and monitor yourself for symptoms.

If you can’t quarantine while awaiting test results:

  • Wear a facial covering around others (even in your own household).
  • Keep your distance from others.
  • Wash your hands frequently.
  • Wipe down frequently touched surfaces throughout the day.
  • Monitor yourself for symptoms; check your temperature every day.

If you (or a loved one) are experiencing possible symptoms of COVID-19, contact your healthcare provider, who can explain your testing options and point you to a local testing center. If you don’t have a regular healthcare provider, contact your local public health department for testing advice. Individuals who are concerned about possible COVID-19 exposure can also get testing information and advice from a healthcare provider or public health department.

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