Widely available, accurate and appropriately utilized COVID-19 testing
remains one of the keys to successfully responding to the pandemic. On May 21st, I sent an email to the Alliance regarding testing for COVID-19. The email
included the chart to the right which does a nice job of displaying the
various testing modalities on a time-line. This article is an update focusing
on the three categories of testing with a special emphasis on serology
(antibody) testing that your asymptomatic patients may ask you about.
There are 3 broad categories of testing: Diagnostic, Screening and Surveillance.
Diagnostic tests are PCR (polymerase chain reaction) tests used for symptomatic
patients to confirm that your patient’s symptoms are due to active
COVID-19 infection. Screening tests are also PCR tests but are used for
asymptomatic patients. In this setting, a negative test in the clinical
context of absence of symptoms, absence of fever and absence of recent
hi-risk contact makes it highly unlikely that the individual is harboring
active virus and thus is safe for transfer to a facility or to proceed
with elective surgery. Surveillance tests are also performed on asymptomatic
patients to determine if antibodies are present indicative of a prior
exposure to the virus. A positive antibody test is NOT indicative of active
virus. It is this third category to which I would like to devote the rest
of this article.
Patients will be asking you about having COVID-19 testing done. They’ve
read about increasing test availability. They’ve seen ads from commercial
labs like this one:
They may have had a nonspecific illness over the last 3 months and are
now curious as to whether it might have been COVID-19. In general, discourage
your patients from having antibody testing done for 3 reasons:
1. There is no scientific evidence that the presence of COVID antibodies
confers immunity to reinfection
2. Serologic tests have inherent limitations including a significant risk
of false-positive results when disease prevalence is low, which apparently
it is in our community. Even among MWHC associates who have worked with
COVID-positive patients, surveillance
testing has demonstrated that less than 2% have tested positive for COVID
antibodies (which is also a testament to how well we have protected our
front-line healthcare workers).
3. Among some of the serology tests out there, there has been a cross-reactivity
with other coronaviruses, such as those that cause the common cold (thus
also increasing the false-positive rate).
Therefore, as the AMA has stated, there are only 3 appropriate uses for
serology (antibody) testing:
1. Population-level seroprevalence studies (as is being done with our MWHC
associates and which will be extended to first responders in our community)
2. Evaluation of convalescent plasma donors (and even if you have a patient
who has recovered from COVID-19 and is interested in being in donor, there
is no need for you to order the test yourself. Simply refer the patient
to the American Red Cross who will carry the ball from there, including
serologic testing if indicated)
3. Medically necessary, well-defined testing plans for patients working
with physicians (e.g. research studies, perplexing cases).
When discussing COVID-19 testing options with your patients, you can take
advantage of the opportunity to reinforce measures which we now know are
effective in significantly reducing one’s risk of contracting COVID-19
as well as the risk of passing it on to others should they unknowingly
be asymptomatic carriers: wearing face coverings, social distancing, frequent
handwashing and staying home if not feeling well.
Thank you for your continued invaluable services to our
community during these unprecedented times.