Covid testing: what to look for protein, nucleic acid (i.e. RNA, or “molecular test”) or antibodies?

August 25, 2020 Daniel Cosgrove, MD


There are diagnostic tests to detect virus, of which there are two types: molecular or antigen tests. Both use a throat or nasal swab. Molecular tests can detect virus before symptoms. They’re harder to find, and clinics don’t like to tell you (especially if they have the cheaper less accurate one). Then lastly --- different from diagnostic tests --- are antibody tests that check your blood for antibodies to the virus.

· One type of diagnostic test are antigen tests. These screen for virus protein, and they’re reliable only several days after one becomes infected, i.e. they’re good for patients with symptoms: fever, weakness, headache. You might hear about the Quidel Sofia 2, or the BD Veritor. These tests are inexpensive and quick, but they don’t amplify the virus nucleic acid (RNA). So if you’re sick, and you want to know, is this influenza or Corona virus? then these are pretty good tests; they’re adequate (and so are the molecular tests).

· Molecular tests amplify the RNA so they can detect Corona virus early, even before symptoms. The Cepheid machine and the Abbott ID Now are two examples of this better technology. See more below about this.

· Antibody tests are only good to see if that illness you had last month was Covid. They take weeks to become positive. They’re no good for early detection before the family reunion! Antibody tests use blood, either a finger stick or a blood test sent to the lab.

o The rapid diagnostic kits got bad press because they were found to be inaccurate. Lots of companies in China claimed they were great, and many were not. I’m not sure the FDA even allows them now.

o If you want an antibody test, it should be a venous blood draw, and it should sent out to a lab like Quest or Mayo. We’ve done lots of these (we have never used the cheap kits).

Eisenhower Medical Center has the Cepheid machine in their lab. This is a molecular test. It’s very good. However, on their website they tell you: they only want to test you if you have symptoms; you need a doctor’s order; the results are “in a few days.”[i] I put a link to their website as an endnote. So Eisenhower has a reliable test, but access is limited. You can’t have your friends get that before a golf game with you, for example. You can’t check your employees until after they have symptoms, and then wait for results, so information can be after several days of them being contagious.

(Note: You may have heard that Corona virus is not contagious until you have symptoms. The World Health Organization (WHO) said that a few months ago, in late March.[ii] However, we now know that’s not true. The problem with influenza and the Corona virus is that they are contagious during the incubation period, i.e. the time after getting the virus but before symptoms.[iii] I’ve referenced just one of several scientific articles demonstrating presymptomatic spread. Note that this article was published in early March. So as I said in my first email/blog about Corona virus, be careful with the WHO.)

That’s why we were so happy to get the Abbott ID Now test machine. If you’re a WellMax member, we’ll give you the test and you know you have priority. But we’ll make it available to anyone, member or not.

[i] https://eisenhowerhealth.org/patients-visitors/coronavirus-covid-19-what-you-need-to-know/faq/ [ii] https://www.who.int/emergencies/diseases/novel-coronavirus-2019/question-and-answers-hub/q-a-detail/q-a-similarities-and-differences-covid-19-and-influenza?gclid=EAIaIQobChMIr4T2yqqr6wIV8R-tBh2G_wNBEAAYASAAEgJAivD_BwE [iii] https://www.medrxiv.org/content/10.1101/2020.03.03.20029983v1

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