Testing theTests

A crib sheet on COVID testing for the virus and for antibodies

| 06 Jul 2020 | 03:04

It’s almost like being back in high school when there’s this big test coming up and no time or way to study for it. Not to worry. This crib sheet explains all you need to know about the two basic tests for COVID-19 - the first to tell if you have the virus, the second to tell if you had it and recovered.

Start with the letter A for Antigens and Antibodies. The first is something foreign, such as a virus which makes its way into your body, alerting your immune system whose white blood cells begin to churn out the second, immunoglobulins (Ig), Y-shape proteins whose sole aim in life is to recognize, capture and de-fang the invaders.

Diagnostic Tests

There are two tests used to diagnose COVID-19. Both look for antigens in mucus or saliva. The first and most effective is the PCR which stands for polymerase chain reaction, a lab technique in which an enzyme quickly stimulates the replication of zillions of copies of a specific DNA so that a very small sample can be used to identify genetic material in antigens. When done by a professional, PCR is considered the gold standard; some do-it-yourself kits are available but the Food and Drug Administration (FDA) warns they may not be reliable.

The second diagnostic test identifies and tracks proteins in the antigens, producing results within minutes. Unfortunately, it also produces a higher percentage of false negatives, tests which say you don’t have the disease although you really do. One study of an early version of missed 10 percent of the cases it tested. Dick Gottfried, chair of the NYS Assembly Health Committee agrees that no test is 100% accurate, but adds, “for some purposes, a test with a small percent failure rate might be acceptable, like a light switch that works 99% of the time but you need to jiggle it 1% of the time to make it work. But if it will electrocute you 1% of the time, that’s not acceptable.”

Antibody Testing

An antibody test is an after-the-fact event to determine the level of antibodies in your body. The first antibodies, IgM, appear in about two weeks after infection. Next up, a second round of antibodies called IgG, which the experts at WedMD.com explain take about four weeks to appear and usually hang around longer than the others. For an as-yet-unknown reason, men - who appear more likely than women to experience serious adverse effects from COVID-19 - produce more antibodies. As with antigen test, FDA cautions that antibody tests may deliver inaccurate results.

All of which begs the question, should you get tested? The answer: It depends. Timing matters. For example, if you have symptoms of viral disease – fever, coughing, headache, muscle ache – your doctor is likely to suggest testing for antigens. If your symptoms are so severe that you end up in hospital, the testing will almost certainly be done to confirm the diagnosis and plan your treatment. But if you have no symptoms, taking the test on Tuesday may show you COVID-19 free but that doesn’t mean you will be free on Friday, so you’d have to test every single day to be certain of your status. As for antibody testing, there’s that waiting period for the test to be useful.

In the end, Gottfried concludes, testing helps to show whether, where and when COVID-19 infections are rising or falling. Eventually, it may also give doctors a clue to the most commonly asked question, whether COVID-19 antibodies prevent a second infection, and more interesting yet, whether these cells from a person who recovered from COVID-19 can help heal someone newly-infected. It wouldn’t be the first time one person’s blood protected another person’s life.