Thursday, May 14, 2020

Kate Snow story on Covid19 on NBC on May 14, 2020: the issue of false negatives

The story by Kate Snow on May 14, 2020 on the NBC Nightly News (Lester Holt) suggested that the PCR test, especially when administered on patients with recent symptoms, can give false negatives (38% ?)

But, recall also


From Face the Nation on 10 May 2020


MARGARET BRENNAN: The president seems to be doubting the value of testing in the workplace. What's your view?

DR. GOTTLIEB: Well, look, I think testing has value in a workplace, especially when you're dealing with places where there's people who are at higher risk of getting infected. So you think about people who work on a shop floor or in a grocery store. The machine- the antigen-based tests that we're talking about here that was just approved is actually less sensitive than a machine that the White House is using. They're using an Abbott platform. But that flat- platform also has false negatives, meaning that sometimes patients- people are going to have the virus. But the test is going to say they don't. There's machines that are more accurate than that Abbott machine, like the GeneXpert. They take a little longer to perform the test. The reason why the White House prefers the Abbott machine is it gives a result in five to 15 minutes. GeneXpert takes about 45 minutes. And so I think that's why they prefer that platform. But this is why we need to have testing out in the community. This is why we need very accurate tests if we're going to be testing asymptomatic people. In the setting of a doctor's office where someone is symptomatic, using a test that doesn't have very high sensitivity might be OK because the doctor's going to run a confirmatory test anyway. But in the setting of where you're testing people who are asymptomatic, as the White House is doing, and you're trying to catch that- those people who don't have any symptoms, you want a very sensitive test for that kind of a purpose. And that's what we should be using out in the employment setting as well.


Hmmm, the tests in the White House are not the same as in the states?

Note also


DR. GOTTLIEB: Well, it helps solve the challenges. I mean, every test paradigm is a little bit different, has pros and cons. The PCR-based tests, where the states have struggled to get the testing supplies, those are more accurate, but they also take more time and they cost more to perform. The reimbursement is about a hundred dollars. Maybe if you do that at scale, you can get the cost down to fifty dollars. There is point-of-care-based systems like the Abbott machine that the White House is using or the GeneXpert, which is very reliable. Those take a little longer to get a result. Their sensitivity isn't as good as the PCR-based machines, with the exception of the GeneXpert, which is very accurate. These antigen based tests aren't as reliable, meaning they're not as sensitive. So they're going to miss some patients who have COVID. But in the hands of a doctor who already has a high index of suspicion that the patient may have the disease, and if they get a negative test and they still think the patient may be infected, they'll send off a PCR-based test. They allow you to dramatically expand testing. And they're very cheap. They're very easy to perform. And again, most doctors have these machines already in their offices. They're using them for strep throat and flu. The challenge is going to be what the guidance is from the CDC and public health agencies about how doctors test in their offices. If turning over a positive case in your medical office means that you have to do a deep cleaning and quarantine your nursing staff and close your office, doctors aren't going to be testing. And that would be unfortunate because there's a big, installed base of these tests already in place. So CDC has to come out with flexible guidelines on how doctors can protect their offices and protect their staff and also be testing in the community. Because if we can't do that, then we're not going to have access to tests. And the challenge won't be the platforms. There'll be plenty of capacity to perform tests. The challenge will become where can you go get the test?


See also the story about Dr. Salerno in Orange, New Jersey. It suggests that many of the people who should be tested have had difficulties in obtaining tests, a problem Dr. Salerno is trying to rectify. Also, notes that Dr. Salerno refers to the level of testing in New Jersey as 7000 per day.


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