False Negatives Raise Doctors' Doubts About Coronavirus Tests

[Orangesapples 1,954]

https://www.bloomberg.com/news/articles/2020-04-11/false-negative-coronavirus-test-results-raise-doctors-doubts?sref=DOTC0U32&cmpid=socialflow-twitter-business&utm_source=twitter&utm_campaign=socialflow-organic&utm_content=business&utm_medium=social&__twitter_impression=true

 

False-negative results from coronavirus tests are becoming an increasing concern, say doctors trying to diagnose patients and get a grip on the outbreak, as a surprising number of people show up with obvious symptoms only to be told by the tests that they don’t have the disease.

While still more research is necessary to determine the true prevalence of such false-negative results, experts agree that the problem is significant. False negatives not only impede the diagnosis of disease in individual patients and an accurate understanding of the extent of its proliferation, but also risk patients who think they aren't ill further spreading the virus.

Some doctors described situations in which patients show up with clear symptoms such as a cough and fever, test negative, and then test positive later on.  It’s a particular issue in New York, where the disease has likely infected far more than the 174,000 people confirmed through limited testing. At Jacobi Medical Center in the Bronx, doctor Jeremy Sperling says so-called false-negative tests are now a frequent occurrence in the emergency room.

 

[Steeleballz 7,550]

 

      Unfortunately this is the nature of PCR based testing. The most common cause of false negatives in PCR testing is having the sample collected improperly. The second is the amount of virus being shed. Early in infections, PCR testing may be negative. The test itself relies on an initial amount of viral RNA being present and then multiplying that RNA millions of times to get a detectable level.

 

   Anyone who orders a PCR testing has to understand that. Sensitivity for positive results are very high. For negative's, not so much. The test result for Covid-19 that we do actually has that as a disclaimer. Negative results cannot rule out disease. Repeat testing recommended if clinical symptoms indicate.

 

  For symptomatic hospitalized patients, a negative test is repeated immediately. It's also the reason people need two consecutive negative tests to be discharged. For outpatients, the physician should follow up a negative by asking about symptoms, and retesting if indicated. Ideally they will get to where they have a <24 hour turnaround time and better availability for outpatient testing as we do for inpatients. 

[Orangesapples 1,954]

15 minutes ago, Steeleballz said:

 

      Unfortunately this is the nature of PCR based testing. The most common cause of false negatives in PCR testing is having the sample collected improperly. The second is the amount of virus being shed. Early in infections, PCR testing may be negative. The test itself relies on an initial amount of viral RNA being present and then multiplying that RNA millions of times to get a detectable level.

 

   Anyone who orders a PCR testing has to understand that. Sensitivity for positive results are very high. For negative's, not so much. The test result for Covid-19 that we do actually has that as a disclaimer. Negative results cannot rule out disease. Repeat testing recommended if clinical symptoms indicate.

 

  For symptomatic hospitalized patients, a negative test is repeated immediately. It's also the reason people need two consecutive negative tests to be discharged. For outpatients, the physician should follow up a negative by asking about symptoms, and retesting if indicated. Ideally they will get to where they have a <24 hour turnaround time and better availability for outpatient testing as we do for inpatients. 

Yep, that's why the numbers we see might be understating the actual size of the pandemic and the actual number of deaths. 

[Steeleballz 7,550]

3 minutes ago, Orangesapples said:

Yep, that's why the numbers we see might be understating the actual size of the pandemic and the actual number of deaths. 

 

  Yeah, and when it's taking 7 days to get that negative result back, people whose symptoms are improving likely won't want to go back and get the test done again, and people who got worse probably already have a second test done in ER before the first one comes back. I think it still points to the bigger issue being lack of testing availability and poor turnaround time for people getting tested on an outpatient basis. It is better than it was, but still no where near good enough.

[Burnt Reynolds 5,058]

38 minutes ago, Orangesapples said:

Yep, that's why the numbers we see might be understating the actual size of the pandemic and the actual number of deaths. 

Half true.

 

Very understated infection count.

 

Possible understated death count.

 

Very overstated mortality rate.

[OriZ 3,157]

9 hours ago, Steeleballz said:

 

      Unfortunately this is the nature of PCR based testing. The most common cause of false negatives in PCR testing is having the sample collected improperly. The second is the amount of virus being shed. Early in infections, PCR testing may be negative. The test itself relies on an initial amount of viral RNA being present and then multiplying that RNA millions of times to get a detectable level.

 

   Anyone who orders a PCR testing has to understand that. Sensitivity for positive results are very high. For negative's, not so much. The test result for Covid-19 that we do actually has that as a disclaimer. Negative results cannot rule out disease. Repeat testing recommended if clinical symptoms indicate.

 

  For symptomatic hospitalized patients, a negative test is repeated immediately. It's also the reason people need two consecutive negative tests to be discharged. For outpatients, the physician should follow up a negative by asking about symptoms, and retesting if indicated. Ideally they will get to where they have a <24 hour turnaround time and better availability for outpatient testing as we do for inpatients. 

This has also caused a situation where they thought some patients have been "re-infected", although that's likely not the case. The sensationalist media likes to report it that way, just look at this as an example:

 

https://www.telegraph.co.uk/news/2020/04/10/south-korea-reports-recovered-coronavirus-patients-testing-positive/

 

"a blow to immunity hopes" lol

 

Totally amateur. My understanding is what happens here, Even the KCDC said it may have just gotten "reactivated", and it wasn't that they were reinfected but never completely healed. They think it can stay "asleep" at levels we can't detect right now with the tools we have that don't cause an infection.  They retested them very shortly after they were officially considered recovered so it's unlikely that was sufficient time for them to have gotten infected again. Another possible scenario they mentioned was that the test results were simply wrong - there seems to be quite a few false negatives with this test which is why they require two consecutive and now some even require 3 negatives to conclude someone is recovered. They also think there may have been tiny traces of the virus left in people's body after recovering, which doesn't mean they are still sick or contagious but could show up in testing. Basically result could come back positive but there's no infection.  They have also found traces of the virus in feces of recovered people so...All that said. Even if we assumed 1% got reinfected, I don't see that as a "blow to hopes of immunity"

[Steeleballz 7,550]

2 hours ago, OriZ said:

This has also caused a situation where they thought some patients have been "re-infected", although that's likely not the case. The sensationalist media likes to report it that way, just look at this as an example:

 

https://www.telegraph.co.uk/news/2020/04/10/south-korea-reports-recovered-coronavirus-patients-testing-positive/

 

"a blow to immunity hopes" lol

 

Totally amateur. My understanding is what happens here, Even the KCDC said it may have just gotten "reactivated", and it wasn't that they were reinfected but never completely healed. They think it can stay "asleep" at levels we can't detect right now with the tools we have that don't cause an infection.  They retested them very shortly after they were officially considered recovered so it's unlikely that was sufficient time for them to have gotten infected again. Another possible scenario they mentioned was that the test results were simply wrong - there seems to be quite a few false negatives with this test which is why they require two consecutive and now some even require 3 negatives to conclude someone is recovered. They also think there may have been tiny traces of the virus left in people's body after recovering, which doesn't mean they are still sick or contagious but could show up in testing. Basically result could come back positive but there's no infection.  They have also found traces of the virus in feces of recovered people so...All that said. Even if we assumed 1% got reinfected, I don't see that as a "blow to hopes of immunity"

 

  Yeah my assumption was that most people who recovered and tested negative and then positive again were never really recovered. They were recovering and had low levels of virus. Maybe some relapses before recovery, but I don't think people are getting infected a second time that fast.

 

  I actually think this happens with a lot of viruses. It's just that we really don't test people 2 or 3 times for most viruses to see if they have negative results when they are recovering. We certainly see people recovering from the flu sometimes and then start to get worse again.