April 29, 2020
Hey Wise Patients! We thank you for sticking with us as we navigate pools and pools of hastily done studies, information (and misinformation), articles, etc. Never hesitate to send us any questions you may have about COVID-19 whether it’s about infection, safety practices, or even antibody testing, which leads us to our next topic…
antibodies, Antibodies, ANTIBODIES:
COVID-19 Antibody testing has come to Wise Patient. Please read the following section on test accuracy carefully. Testing will occur on Wednesdays and Thursdays between the hours of 11:00am – 1:00pm. If you’d like to be tested, give us a call at (206) 466-5937. Note that our testing is only available for our patients. If you have been forwarded this newsletter and would like more information about joining Wise Patient, please click here to learn more and/or here to sign up.
SARS-CoV-2 antibody testing accuracy, best we know it:
The University of Washington Virology Lab has approved Wise Patient to send them your blood samples for SARS-CoV-2 IgG antibody testing using Abbott’s chemiluminescent microparticle immunoassay. UW Virology Lab will bill your insurance or you can pay $44.10 to us to pay UW directly (no profit to us, explained below).
SARS-CoV-2 IgG antibodies are produced in the late stages of COVID-19 infection and may remain in the bloodstream for months or even years. Abbott claims their test, when performed at least 2 weeks after a patient’s initial symptoms of infection, has a sensitivity of 100% and specificity of 99.5%. In a news interview, Dr. Alex Greninger, Assistant Director of UW Medicine Virology Lab, described sensitivity of 100% and specificity of 99.6%, based on 1200 specimens tested internally by Abbott (unpublished, therefore we don’t know anything about the 1200 specimens).
Please carefully ingest these consumer awareness facts:
Accepting this test’s accuracy as reported by Abbott involves exceptional trust in Abbott and in UW’s vetting of the myriad tests before choosing this one. When other than the COVID pandemic would we need to rely on a Geekwire article (https://tinyurl.com/y8a4qwlo) and KIRO-TV interview with UW Virology (https://tinyurl.com/y9lnpgr4) as primary sources of a test’s accuracy, rather than peer-reviewed validation testing published in scientific journals! This is because the FDA, balancing haste with caution in mid-March, waived their core requirements for accuracy testing for these tests. None of them are “FDA approved” as we know it). Our strong wish is for confirmatory testing of this and other tests, performed by academic centers and agencies (FDA, CDC, and NIH) in the near term.
If you are trying to avoid a “false-positive” result, where the test says that you are a ‘recovered’ case of COVID-19 but in reality you never had COVID-19, a high test specificity is what you are after, and even decimals matter. A specificity of 99.5% was reported to have been reported by Abbott (https://tinyurl.com/y9xknuet) based on the 1200 specimens they tested, and Dr. Greninger quoted a specificity of 99.6% to KIRO-TV. This is the highest claim of specificity we have seen reported among the antibody tests on the market thus far. Most of the antibody tests flooding the market will fail because of false-positive results (say, from past exposure to one of the common cold coronaviruses rather than SARS-CoV-2).
No proof of immunity if you are IgG+. A person’s level of protection from reinfection once they are SARS-CoV-2 IgG positive is unproven. The data needed to figure this question out will require some observation time since it seems unethical to study by throwing virus in the faces of brave IgG+ volunteers (right?). Throwing virus in the faces of a small number of macaque monkeys was unable to reinfect them (https://tinyurl.com/yx5nfopy) and most scientists’ statements we have read in the press suggest good reason to believe COVID-19 survivors to have some immunity to the virus. How strong? How long? Who knows?
What is the chance of a false-positive result? Look how many more false-positives occur when the specificity of the test drops even a bit. Look how many more false positives occur when the fraction of people being tested who truly had COVID-19 (so called true-positives) is lower.
Scenario 1: If 5% of the population being tested truly are recovered from COVID-19 infection (aka 5% prevalence).
With the Abbott test UW is using (assuming 100% sensitivity, 99.5% specificity), for every 50 true-positive results (you people really did have COVID-19) there will be an additional 4.75 (OK, call it 5) false-positive results (test indicates you had COVID-19 but you really didn’t). Means 8.7% of all positive results will be false-positives.
If we decrease the specificity from 99.5% to 98%, for every 50 true-positive results there will be an additional 19 false-positive results. Means 27.5% of all positive results will be false-positives!
If we decrease the specificity further, to 96%, for every 50 true-positive results there will be an additional 38 false-positive results. Means 43.2% of all positive results will be false-positives!
Scenario 2: If 10% of the population being tested truly are recovered from COVID-19 infection (aka 10% prevalence), the percentages of all positive results that will be false-positives in the above examples become: 4.3%, 15.3%, 26.5%.
Scenario 3: If 15% of the population being tested truly are recovered from COVID-19 infection (aka 15% prevalence), the percentages of all positive results that will be false-positives in the above examples become: 2.8%, 10.2%, and 18.5%.
OK, you get it, most people would find the false-positive rates of the ‘less specific’ tests that have flooded the market to be unacceptable, even with specificity of 98% and a true-positive prevalence of 15% (higher than most predictions for Seattle). In fact, some people would find the false-positive rates of the UW/Abbott test to be unacceptable for their specific purpose is in seeking the test. Your judgement is required. No test is perfect, but given the circumstances of COVID-19, we believe the option to obtain this antibody test should be yours. Our role is to help you interpret the test to the best we can.
Some final points:
Again, none of the antibody tests are “FDA approved” in the classic rigorous sense.
Here is a helpful compilation SARS2-CoV-2 antibody tests John Hopkins put out and says they will update twice per week: https://tinyurl.com/y9sesy6a. Control-F to search for the test you are being offered.
If you feel the need to get an antibody test elsewhere (more convenient, you’re out-of-town, etc), please first send us the reported sensitivity and specificity of the test, so we can inform you of its calculated false positive potential under different prevalence scenarios (offer only applies to our patients btw, owed to time constraints). If you can’t find any report of sensitivity and specificity, don’t use that test.
We didn’t discuss the potential for false-negative test results above for two reasons: i) We didn’t want to distract you from focusing on the false-positive potential since that is the error with the higher stakes in most circumstances (believing you have already been infected when in fact you have not); and ii) It approaches zero IF the claim of 100% sensitivity holds true (admittedly we feel weird saying “100%” and “medical test” in the same sentence).
On IgM antibody testing. The IgM antibody is produced earlier than the IgG antibody, and is generally detectable several days after initial infection. If the test you are considering is combined IgM and IgG, the company should report sensitivity and specificity for IgM and IgG separately.
Your cost for this UW Virology IgG test: For you early (insured) testers, please let us know how the billing to your insurer for this antibody test plays out to give us a sense of common out-of-pocket costs, if any. For those who opt for cash pricing, we will run your credit card here in clinic for $44.10, which will cover the $42.00 UW will invoice us (they refuse the headache of cash billing themselves) plus the revenue-based taxes and administrative costs (such as driving your blood samples to UW). We do not want to profit from offering this test.
If you have had a documented COVID-19 infection, you don’t need antibody testing.
- We don’t yet have a good sense for turn-around time for your test result, but that should become pretty clear pretty soon.
It’s OK to go outside!
If you’re like us here at Wise Patient, you’ve been wanting to get outside for the fresh air, the exercise, and the mental health boost it gives you. Maybe you’ve already been getting outside and want to know if that’s really ok. Maybe you’ve gotten side-eye from your neighbor for doing it (I see you looking at me, Gary, I see you!) There’s debate about whether you can get COVID19 while you’re at your favorite park or, more controversially, from runners exhaling apparently long trails of unicorn sparkles respiratory
Pets of Wise Patient
We’ll kick it off with photos from our team this week, but we would love to feature patients’ pets in the future. Send us goofy and heart-warming photos over Spruce so the whole community can enjoy. (All animals welcome!)
And remember… WASH YOUR HANDS!
Reliable Sources to Stay Updated on the COVID-19 Outbreak
- A comprehensive list of resources is available on last week’s newsletter which is available on our website:
If you have any questions, please contact our office at: firstname.lastname@example.org