When they say test results are 15 percent false negative...

[Jeebo]

...how do they know that? If 15 percent of those negative results are false, and if the tests are the way they find out whether somebody has it or doesn't have it, and if they somehow KNOW that 15 percent of the results show the person doesn't have it when s/he actually does have it, then there must be some OTHER way besides the tests for them to know whether somebody has it or not. In that case, what good are the tests? What do we need them for? Why not rely on that OTHER way of knowing whether somebody has it or not, whatever that other way is? I don't understand.

-- Ron

[blm]

1. Covid 19 can be determined with Lung x-rays

[thesquanderer]

4. Autopsies, too. (n/t)

[Jim__]

2. Here's one way:

From NPR:

The fastest test being used to diagnose people infected with the coronavirus appears to be the least accurate test now in common use, according to new research obtained by NPR.

Researchers at the Cleveland Clinic tested 239 specimens known to contain the coronavirus using five of the most commonly used coronavirus tests, including the Abbott ID NOW. The ID NOW has generated widespread excitement because it can produce results in less than 15 minutes.

But the ID NOW only detected the virus in 85.2% of the samples, meaning it had a false-negative rate of 14.8 percent, according to Dr. Gary Procop, who heads COVID-19 testing at the Cleveland Clinic and led the study.

"So that means if you had 100 patients that were positive, 15% of those patients would be falsely called negative. They'd be told that they're negative for COVID when they're really positive," Procop told NPR in an interview. "That's not too good."

more ...

[Maeve]

3. They test them on known samples

Before testing on humans, they test on known samples of the virus. There are also other issues--this from the BBC--

The only thing worse than no test is a test that’s wrong. Laboratories can only start testing patients after they have done sufficient studies to ensure reliability. These tests usually take upwards of six weeks, but technicians have been working double shifts to speed the process.

To make matters more complicated, sometimes a patient can test negative even when they’re sick. They may have the virus in their lungs, but no longer release it near the nose where it would stick to the swab. Or, the sample was not obtained correctly.

Of course, this all describes swabbing as a means of searching for a live virus in the patient.

But the latest buzz in testing is the blood test: the antibody or serology test, which could be used to establish if someone had the disease in the past and developed immune cells to recover from it. It detects one specific part of a patient’s immune response to the disease – the presence of antibodies. It is hoped these proteins might protect patients from reinfection, although any protection remains to be seen.

Devising an accurate antibody test ushers in a whole new set of challenges. It must ensure that it’s spotting the precise immune cells that fought this particular germ, and not some run-of-the-mill coronavirus, like the common cold. And some people might recover from the disease without ever developing antibodies.

https://www.bbc.com/future/article/20200422-why-are-coronavirus-tests-so-difficult-to-produce

[fescuerescue]

5. There are other ways to determine the infection

Folks who are sick but test negative continue to BE sick.

This prompts doctors to look deeper and they have found that 15% of those that continue to be sick, do indeed have COVID19.

Naturally this extrapolates to rest of population.