COVID19 Testing

Saugatuck Pediatrics has the ability to do in house lab based COVID19 testing (different from and more sensitive than the over the counter rapid tests).  One test is a rapid lateral flow assay made by Quidel and run on a Sofia platform (what we use for our flu testing as well.)   The test is most accurate in children with symptoms (day 3 the best) or on days 3-5 following a COVID exposure. We also have the Abbott Molecular NAAT testing, which is close in accuracy to a PCR test.  PCR testing is a send out lab that can take 24-72 hrs for results.

All our COVID19 tests are done with an easy “nose tickle” anterior nasal swab (gone are the “brain samples” of the past where we had to do a deep nasal swab.)

Should I trust rapid tests?

Rapid tests are currently only indicated for use as nasal swabs- suggestions to use then as throat or oral swabs are discouraged due to lack of evidence that these methods are supported. Saliva has a different pH than nasal secretions,which may affect results.

VERY USEFUL ARTICLE ON VALIDITY AND WHEN TO USE RAPID TESTS by Your Local Epidemiologist.

When is a COVID test indicated? 

We know that COVID symptoms can mimic almost any other infectious illness.

  • Sick symptoms associated with COVID will require testing downstairs prior to being seen in the office (this includes any respiratory symptoms, gastrointestinal symptoms such as nausea/vomiting/diarrhea, and fever.)
  • Possible exposure + ANY symptom would also trigger testing.
  • Household exposures should be tested as soon as a family member is diagnosed.
  • Non-household exposures should be tested on days 1, 3 and 5 post exposure.

Nasal Swab (acute illness testing)

There are two types of COVID19 acute testing (looking for presence of the virus in the mouth or nasal passages.)  PCR tests detect genetic material of the COVID-19 virus, and are done in complex hospital and commercial labs.  These are very sensitive but may have a lag time for results. Antigen tests rapidly detect certain proteins that are part of the COVID-19 virus. These tests require a higher viral load to detect infection, but have a much faster turnaround time allowing us to properly quarantine those infected and exposed, and do more efficient contact tracing (see article here and article here addressing rapid tests as the best way to control the pandemic).

If your child tests negative with the rapid antigen test, but shows classic signs of COVID19, we may recommend PCR testing and quarantine until the more sensitive test results are known.


COVID19 Antibody Testing

Antibody testing on blood specimens can both confirm suspected cases after the fact, and also reveal who was infected and didn’t know it. We believe anywhere from 25-50% of people with SARS-CoV-2 infection may have mild or no symptoms. At this point in the pandemic, just about everyone in the US has likely had at least one case of COVID19- only IgM testing would show acute disease, IgG would only show if you had the disease in the past, and cannot guarantee that you will not get infected again.

Antibody tests look for either IgM (an antibody that appears early in the disease), IgG (an antibody that may take 10-14 days to develop), or test for both IgM and IgG. IgM may only last a few weeks after infection, while IgG typically lasts for months (in the case of influenza) to years (in the case of measles).

Here is a Cochrane review of the accuracy of COVID19 antibody tests. (Cochrane is a global independent network that gathers and summarizes the best evidence from research to help you make informed choices about treatment). The review shows that antibody tests could have a useful role in detecting if someone has had COVID-19, but that timing is important. The tests were better at detecting COVID-19 in people two or more weeks after their symptoms started, but we do not know how well they work more than five weeks after symptoms started. We do not know if this is true for people who have milder disease or no symptoms, because the studies in the review were mainly done in people who were in hospital. In time, we will learn whether having previously had COVID-19 provides individuals with immunity to future infection.

Here is a review of how COVID19 immunity may work, and why there are limitations to antibody testing.

Here is an overview of COVID19 antibody testing from the CDC.​

What are the limitations of antibody testing? 

  • If the antibodies provide protection, we don’t know how much and for how long.
  • The tests also vary in which specific antibody is tested; COVID19 has both a nucleoprotein (N protein) and a spike protein (S protein) that we can react to. We don’t know which antibody will ultimately prove effective against repeat exposures.
  • Role of T-Cells in Immunity  Many patients infected with COVID-19 don’t seem to develop antibodies, or the antibodies wane over several weeks to months.  However, this doesn’t mean we don’t have lasting immunity- T-cells are a type of white blood cell that has a memory of sorts for past infections, and may help the body kick off antibody production when re-exposed to a prior infection.  Vaccines that result in specific T-cell production as well as antibodies could offer long lasting protection.

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