Once I feed the cats and finish posting this post, I am going to donate blood. I am O+ without CMV which evidently makes the hematologists very happy to schedule me on a regular basis. One part of the e-mail campaign for this donation was a promise that my blood would be tested for COVID-19 antibodies and I would be notified of the results in a week.
I can understand why the blood bank wants to screen for COVID as a means of insuring a safe blood supply. However we can’t think that the numbers will tell us much about a region’s COVID exposure. This is attractive but almost useless for systemic surveillance.
Blood donors are a self-selected population. Before donating blood, a donor has to have answered over forty questions of a basic current health and long term medical history. One of the knock-out questions is if you have had the cold or flu recently. Screening blood for COVID antibodies might allow for a plausible lower boundary of regional infection history. This population is likely to notable underestimate disease prevalence.
The other challenge that we need to be aware of if any blood donor infection and recovered figures are released is the problem of false positives. If we assume that the blood donor population that is screened is likely to have a lower than population average incidence rate, than we also have to assume that a higher proportion of the reported positivity rate is false positives. If we assume that a regional cumulative COVID prevalence rate is 10% and the test returns 1% false positives and no false negatives, than the false positives will be about 8% of the total reported positives. If we assume prevalence is 5% then the false positives are 16% of the reported positives. If we assume prevalence of 2.5%, 29% of the total reported positives are false positives. The Positive Predictive Value of the tests that have Emergency Use Authorizations (EUA) from the FDA are frequently below 90% if we assume a 5% population prevalence.
Since we are assuming that blood donors are less likely than the general population to be infected, the value of the testing result being reported back to the individual donor is going to be low.
And this is problematic. If someone receives notification that they have COVID-19 antibodies, they are likely to act on that information and engage in behaviors that are more likely to increase spread risk. If they are truly immune, this is not a big deal. But if they are not immune, they are more likely to be an unsuspecting spreader during a non-symptomatic phase of a future infection.
Communicating these types of results for a low incidence but high impact disease is tough as the information is likely to change behaviors.
Mousebumples
Thank you for being a blood donor!
I agree that test results (antibody or live viris) can adversely impact the actions of the population. As we saw with the White House staff (not the brightest, granted), a negative test (especially regular negative tests) can lead to poor risk related choices.
And a positive antibody test, until we know more about the duration of immunity, could be similarly dangerous.
I’m a scientist, and the multitude of unknowns are not great for my anxiety about all this. >_>
Barbara
Why does your CMV status matter? I know mine is positive.
azlib
I regularly give platlets (every 3 weeks) and occasionally some red blood cells. I asked about COVID-19 testing and the blood center here apparently does not do testing locally. Your point about biased samples is well taken, but it would be nice to know if I had been infected. I am well aware of the problem with false positives or negatives. I had a bad sore throat and cough in early February which I may have caught something on a plane ride at the end of January. Could have been almost anything and not COVID-19.
DAVID ANDERSON
@Barbara: cmv- is good for babies
Brad F
One of my residents asked me the other day, “exactly what test is the gold standard against which the EUA tests are being compared…and oh, btw, I have not heard of anyone characterize any Ab screening test as perfect.”
When path or tissue confirmed specimens are the gold standard, that’s home run. Have done quick Googles on above question, but have not found an answer. I am assuming the FDA has the golden machine, but I want to confirm. Anyone reading, please weigh in.
Brad
Barbara
@DAVID ANDERSON: Right. That is how I know I am CMV+, because they were concerned my premie had been exposed to an infection. She tested negative but I was positive so that wasn’t it.
Mousebumples
CMV status can also be important for the immunocompromised. There are specific antiviral treatments for CMV- organ transplant recipients that get a CMV+ organ, for example.
Soprano2
Not about blood, but I’ve seen several articles now about wastewater testing for the virus. They can forecast outbreaks and which part of a city they’re occurring in at least a week before people start showing up at hospitals. Many larger systems already have their service area divided up into sewersheds, so it would be relatively easy to test at these spots weekly. It has the beauty of not depending on people to get tests and getting results from everyone because we all use the sewer! It could help hospitals and city officials better understand what’s going on in their cities. It’s already been done for other diseases and for drugs.
David C
@Mousebumples: Also CMV negative. I’m always careful to make sure I don’t have any kinds of symptoms. To schedule an appointment they are asking additional questions about wellness and contact with possible Covid carriers.
Planning to head to the NIH Clinical Center for a donation next week – they have all kinds of precautions to get into the building, but AFAIK they don’t do any antibody testing.
Anonymous At Work
B-, blood bank administrators are on a first-name basis and have the 8-weeks marked out on calendars.
Happy to do it, but other health things interfering.
dimmsdale
I appreciate your posting this, David. I’m an O positive blood donor (greater NY blood program; they do NOT test for COVID) and got screened recently by Columbia University for plasma donation–the screening was the standard blood-donation screening plus survey questions about COVID-specific symptoms. I’m also getting somewhat desperate-sounding entreaties from the blood program about donating (since elective surgeries have resumed) but wanted to hold off till I knew exactly what my status was wrt the virus and if I have antibodies present. (Columbia is supposedly setting up both a nasal-swab test and a serum blood test but I haven’t heard back from them about that yet.)
As to behavioral changes as places open up, I think people who are NOT idiots are going to wait for either a vaccine OR some reliable ameliorative protocol (hydroxycholoquine, remdesevir, whatever) that would cut the destructive effects down to an acceptable level (IF such a thing exists). I have an in-office doctors appointment next week, my first foray outside of a 5-block radius of my apartment since the lockdown in mid-March–and will assess levels of hazmat that I see being practiced, to determine how freely I move around in the future (this includes prevalence of mask-wearing, which to me is essential).
Is it possible, I’m wondering, that an ameliorative protocol could exist that actually WOULD make catching the virus no more burdensome than, say, mild flu? (This wouldn’t apply to people with serious comorbidities, of course, and even if I could take a pill that would make the virus merely unpleasant rather than fatal, I’d still be in danger of transmitting the virus to much more vulnerable people. Given THAT, the only way I’d feel freer to move around would be if I felt reckless and utter disregard for others I might infect–which applies to more of the population than I would wish, I’m afraid.)
MiLilvies
I used to donate a lot. I mean a lot – gallons. But I found our local Red Cross donor center was always disorganized. They’d try to recruit me before the 8 weeks were up, would screw up data regularly and I found the donor center too dirty for my tastes (and I have a relatively low bar).
I won’t be donating since they told me I was too old (but couldn’t explain what the age was!) and I would be afraid of catching something going there now.
Sad.
sstarr
I have never donated blood, because I lived in England during the MAD COW outbreak. A couple of weeks ago, hearing about the problems with the blood supply I checked again, and they still don’t want my prion infected blood. MOOOOO.
Hilfy
You have it backwards. FEED CATS FIRST, then write posts or other unimportant human tasks. So says my Lucky and Henry.
Carlo
It seems a bit odd to me that they should test donated blood for SARS-CoV-2 antibodies, but not for viral RNA. I would have thought it much more important to know that no blood was donated by an asymptomatic infected person than to get a (biased) view into the recovered fraction of the epidemic. Perhaps RT-PCR tests are only set up for swabs rather than blood (although I know of saliva testing efforts too). The CDC Instructions for such tests (fda.gov/media/134922/download) assert in effect that the false positive rate is too small to measure.