Volume 35 Number 2 | April 2021
Patient Safety Corner
Brandy D. Gunsolus, DCLS, MLS(ASCP)CM
The COVID-19 pandemic has done many things, including shining a spotlight on laboratory testing like it has never had before. Unfortunately, what it has also brought is much confusion as both clinicians and the general public struggle with what is considered a “good” test and what is not. The Food and Drug Administration (FDA) did little to address the confusion as it gave a mostly blanket approval of any test whose manufacturer bothered to file the paperwork. Yet, it is the patients and the general public who have suffered.
Early on, I and many other laboratory professionals spent much time explaining the difference between PCR and antigen tests, explaining why you should never use PCR as a test for cure, and much more. Unfortunately, the media, with little knowledge of the PCR testing that is actually used in clinical laboratories, continues to spread misinformation regarding the test. Like trying to explain that the Earth is not flat, we do not have PCR tests utilized in CLIA-certified clinical laboratories that perform PCR to 65, 80, or infinite cycle counts.
When COVID antibody testing came to market in April, we had another onslaught of misinformation, from antibody passports to IgG vs IgM vs IgA. Clinicians were confused, as was the public. As laboratorians, we weren’t really sure what to do with this test. A positive test indicates you had a previous infection with SARS-CoV-2 virus, and you had an antibody response. We didn’t know what that antibody response really meant. But the pandemic continued, and we learned more.
“As this virus continues to mutate, we, as laboratorians, must stay on our toes.”
Now we have learned that generally you are no longer transmissible after 12 days. We know that most people will have an antibody response, but some people with asymptomatic or very mild infections have little to no antibody response. We know that post-disease antibodies last for three to five months. This has allowed us to find a new use for SARS-CoV-2 antibody tests, but we need to be careful which test we use.
The lateral flow tests often have many interferences and tend to have both lower specificity and lower sensitivity than their EIA or ELISA comrades. But even in the EIA and ELISA cohort of SARS-CoV-2 antibody tests, one must read the package insert and understand what they are truly measuring.
I will give you an example from my own facility. For supply chain reasons, we validated SARS-CoV-2 IgG on two different platforms: DiaSorin Liaison XL and the Abbott Architect. The tests correlated well against each other and all seemed fairly interchangeable. Once there was literature showing when transmission of the virus ceased and when IgG antibodies formed, we began using the antibody test to determine which inpatients were still contagious and needed to stay on contact precautions, and which patients were far enough in their disease course to come off contact precautions, thus reducing the use of our very limited PPE and helping us bed patients in the hospital more appropriately.
When we began vaccinating, we started receiving requests to monitor immune response to the vaccine. Some was for research, others for clinical purposes. However, all were negative on the Abbott platform unless they previously had documented infection with the virus. But there is clear reason for this: the Abbott Architect detects IgG antibodies to viral nuclear envelope. The DiaSorin Liaison XL detects IgG antibodies to the spike protein. The vaccine causes the immune system to produce antibodies to the spike protein, therefore, post-vaccination antibodies could not be detected on the Abbott Architect, but were detected on the DiaSorin Liaison XL. We now run SARS-CoV-2 IgG continuously on both platforms: one as a general antibody targeted for post-disease use and the other for post-vaccination immune response.
As this virus continues to mutate, we, as laboratorians, must stay on our toes. Will the PCR platforms we currently run detect all variants we have now and those yet to come? Will our tests change to be more like influenza testing, where we can report the different variants identified? Too early to tell. For myself, I will stay vigilant.
Reference
Galipeau Y, Greig M, Liu G, Driedger M, Langlois M. Humoral Responses and Serological Assays in SARS-CoV-2 Infections. Frontiers in Immunology. Dec 2020. doi: 10.3389/fimmu.2020.610688
Brandy Gunsolus is Doctor of Clinical Laboratory Science at Augusta University Medical Center in Augusta, Georgia.