5 ms·

Couple of thoughts: - I think we need to know a LOT more about the sensitivity, specificity, and accuracy of every test that's being deployed right now. I am

Couple of thoughts: - I think we need to know a LOT more about the sensitivity, specificity, and accuracy of every test that's being deployed right now. I am 100% willing to believe that "testing negative and then positive" means "you have a pretty low viral load and our tests suck more than we're willing to admit out loud right now". - I think we need to be very clear that there are two kinds of tests: "you have an active SARS-CoV-2 infection right now, and also "you have once had a SARS-CoV-2 infection in the semi-recent past". One tells you who needs care, one tells you who is at least temporarily immune we hope.

dboreham 7y ago
The article mentions RNA implying that this is the PCR test not an Antibody test. False positives exist with the PCR test. Information I could find suggests the primary cause is sample contamination. So running the test multiple times through different labs and clinicians is an obvious workaround.
- frabbit 7y ago
  Surely this is not a false-positive, but rather a false-negative? That is, the patients were observed clinically to have caught and recovered from the virus, yet the test shows no trace of the viral infection.
  - lostlogin 7y ago
    > Surely this is not a false-positive, but rather a false-negative? Both are possible and either mess it all up.
    - unwoundmouse 7y ago
      This is the correct answer
  - deleted 7y ago
    [deleted]
- dnautics 7y ago
  More likely sample degradation as well. Rna is notorious for being extremely fragile exactly when you need it not to be and extremely robust when you don't. Academic rna labs have a reputation for being clean freaks, and there was a spate of spurious observations when rt(rt)pcr became a thing ten or so years ago... I'm still not convinced of rt/rt results performed by run of the mill labs, generally speaking.
baxtr 7y ago
In general PCR tests are highly sensitive. Even smallest viral loads can be detected (Edit) added in general above due to valid points in the comments below
- hprotagonist 7y ago
  if: - you do them right - your reagents are good - the kit was assembled properly - there's no contamination in the machines - you got a good sample - ... The capability for a highly sensitive and accurate test in no way guarantees that a randomly sampled administration of that test is going to meet the high standard that the test may be capable of.
  - twic 7y ago
    And if you swabbed an infected part of the body in the first place! In 205 patients with proven COVID-19 [...] bronchoalveolar lavage fluid was positive in 14/15 (93%), sputum 75/104 (72%), nasal swabs 5/8 (63%), brush biopsy 6/13 (46%), pharyngeal swabs 126/398 (32%), feces 44/153 (29%), blood 3/307 (1%), and urine 0/72 (0%). https://www.jwatch.org/na51116/2020/03/17/pharyngeal-and-nasal-swabs-may-not-have-adequate https://www.jwatch.org/na51116/2020/03/17/pharyngeal-and-nas...
    - hinkley 7y ago
      Hol' up. > blood 3/307 (1%) Why isn't their blood rotten with virus?
      - gojomo 7y ago
        I suspect it's because this virus is optimized to enter cells that line the lungs/respiratory tract, then also sheds back that same way. Meanwhile, cells in, and along, the bloodstream aren't infected – and are most-trafficked by the body's immune response, including virus-destroying antibodies. (Why are rodents more prevalent in the walls/crawlspaces of a dwelling, rather than the hallways?)
deleted 7y ago
[deleted]
Spooky23 7y ago
Even a common well established test like a quick strep test has a significant (10% iirc) false negative rate. I'm sure that a rapidly developed test to an emerging target is going to have a significant error rate.
klmadfejno 7y ago
Suppose you get the disease and develop antibodies for it. Your body is pretty darn good at fighting the virus and won't get sick from it easily. But, you're in a place with a huge viral load exposure. Wouldn't that imply there should be some of the virus in your lungs? Test accuracy aside, is the definition of "positive" even clear?

dboreham 7y ago

The article mentions RNA implying that this is the PCR test not an Antibody test. False positives exist with the PCR test. Information I could find suggests the primary cause is sample contamination. So running the test multiple times through different labs and clinicians is an obvious workaround.

frabbit 7y ago
Surely this is not a false-positive, but rather a false-negative? That is, the patients were observed clinically to have caught and recovered from the virus, yet the test shows no trace of the viral infection.
- lostlogin 7y ago
  > Surely this is not a false-positive, but rather a false-negative? Both are possible and either mess it all up.
  - unwoundmouse 7y ago
    This is the correct answer
- deleted 7y ago
  [deleted]
dnautics 7y ago
More likely sample degradation as well. Rna is notorious for being extremely fragile exactly when you need it not to be and extremely robust when you don't. Academic rna labs have a reputation for being clean freaks, and there was a spate of spurious observations when rt(rt)pcr became a thing ten or so years ago... I'm still not convinced of rt/rt results performed by run of the mill labs, generally speaking.

baxtr 7y ago

In general PCR tests are highly sensitive. Even smallest viral loads can be detected (Edit) added in general above due to valid points in the comments below

hprotagonist 7y ago
if: - you do them right - your reagents are good - the kit was assembled properly - there's no contamination in the machines - you got a good sample - ... The capability for a highly sensitive and accurate test in no way guarantees that a randomly sampled administration of that test is going to meet the high standard that the test may be capable of.
- twic 7y ago
  And if you swabbed an infected part of the body in the first place! In 205 patients with proven COVID-19 [...] bronchoalveolar lavage fluid was positive in 14/15 (93%), sputum 75/104 (72%), nasal swabs 5/8 (63%), brush biopsy 6/13 (46%), pharyngeal swabs 126/398 (32%), feces 44/153 (29%), blood 3/307 (1%), and urine 0/72 (0%). https://www.jwatch.org/na51116/2020/03/17/pharyngeal-and-nasal-swabs-may-not-have-adequate https://www.jwatch.org/na51116/2020/03/17/pharyngeal-and-nas...
  - hinkley 7y ago
    Hol' up. > blood 3/307 (1%) Why isn't their blood rotten with virus?
    - gojomo 7y ago
      I suspect it's because this virus is optimized to enter cells that line the lungs/respiratory tract, then also sheds back that same way. Meanwhile, cells in, and along, the bloodstream aren't infected – and are most-trafficked by the body's immune response, including virus-destroying antibodies. (Why are rodents more prevalent in the walls/crawlspaces of a dwelling, rather than the hallways?)

deleted 7y ago

[deleted]

Spooky23 7y ago

Even a common well established test like a quick strep test has a significant (10% iirc) false negative rate. I'm sure that a rapidly developed test to an emerging target is going to have a significant error rate.

klmadfejno 7y ago

Suppose you get the disease and develop antibodies for it. Your body is pretty darn good at fighting the virus and won't get sick from it easily. But, you're in a place with a huge viral load exposure. Wouldn't that imply there should be some of the virus in your lungs? Test accuracy aside, is the definition of "positive" even clear?