3 Different Covid-19 Tests. Who Needs Which and When?

cartoon of Dr. Mimi Guarneri studying covid tests

3 Different Covid-19 Tests. Who Needs Which and When?

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by Mimi Guarneri, MD, FACC

Today, three different Covid-19 tests can help you know whether:

  • you may have had Covid-19 in previous months and been asymptomatic
  • a serious illness you experienced before was indeed Covid-19
  • the illness you’re currently suffering is Covid-19

Depending on which you suspect, your doctor will recommend one of the three tests. For those outside the medical community, it’s a struggle to understand whether you should get the Covid-19 antibody test, the Covid-19 antigen test, and the Covid-19  PCR test.

We offer all three at the Pacific Pearl La Jolla. Call 858-459-6919 to discuss your options, but read below first.

The Covid-19 Antibody Test

This blood test reveals whether a person has already been exposed to Covid-19 by detecting specific antibodies unique to this virus in their blood. Doctors do not use antibody tests to diagnose current, active infection. The body takes time to produce antibodies, after all.

False-negative test results occur only if the test is taken too soon after infection and before the body has had the chance to make Covid-19 antibodies. False-positive tests can occur sometimes when the individual has experienced a previous infection involving other coronaviruses that are not Covid-19 specifically.

Here at the Pearl, we use the antibody test with patients who report prior fever, cough, fatigue, and other Covid-19 symptoms. In fact, since we began testing in early April, we’ve found 40% of patients reporting these symptoms did test positive for Covid-19.

How Long Do Antibodies Last?

Study outcomes differ on the window of protection Covid-19 antibodies provide. Data from the journal Nature found antibody levels beginning to wane after two months. A recent study from the University of Oxford and Oxford University Hospitals (OUH) NHS Foundation Trust concluded that protection could be as long as six months. It is too early to know.

The Covid-19 Antigen Test

An antigen test reveals if a person is currently infected with Covid-19. Using a long swab, the practitioner takes a fluid sample from the back of the patient’s nasal passage or throat.

Antigen tests detect the “spike” proteins found on the surface of the Covid-19 molecule. Once the infection has left the body, none of those proteins will remain. Antigen tests provide rapid results, often in under 20 minutes. They are less accurate than the PCR test below.

The Covid-19 PCR Test

This COVID-19 test detects Covid-19 genetic material through a lab technique called “polymerase chain reaction” (PCR). As with the antigen test, the practitioner takes a fluid sample from the patient’s nose or throat with a long swab as asks them to spit in a tube. The sample is sent to a lab and the patient receives results in days, depending on the lab’s backlog of samples. Properly performed PCR tests are more accurate than the antigen test, but these tests take longer to perform and can return false-negative results.

We offer all three tests at the Pacific Pearl La Jolla. Call 858-459-6919 to discuss your options. We are happy to help!

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