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October 21st, 2020 11:32 AM #18601
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Tsikoteer
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October 21st, 2020 11:55 AM #18602first off, these two statements say it all for covid:
a negative antibody test should not be equated with absence or presence of the virus in the body.
neither should a positive antibody test be equated with the presence or absence of the virus in the body.
"ANTIGEN" refers to the virus itself or parts of it.
a number of PCR tests are designed to detect the spike protein, the nucleic acid, or other components of the covid virus. the test material is usually from a (painful) a swab of the patient's posterior nasopharyngeal wall.
because of the intricacies of the testing procedure, detection of covid virus antigens is traditionally slow, requiring several hours of table work.
a problem we now realize, is that even as the virus is already dead or non-viable, some of these virus components may be still around, and might detected by the test, resulting in a "false positive" result.
there are more rapid tests emerging now, needing 30-60 minutes only. there are even the more convenient rapid saliva tests that are promising to be potentially as good as the traditional gold-standard PCR.
when our immune system detects the virus, they manufacture "ANTIBODIES".
antibodies are proteins that correspond to the virus. they are very specific, akin to the specificity of keys to their padlocks.
but... just like keys and padlocks... sometimes, just sometimes, another key might be able to open its un-intended padlock. the so-called "cross-reaction".
(OT. do we remember the 80s, where it was rumored that a lancer key could open one in eight lancers in the parking lot? heh heh.)
antibody tests are much easier to effect. by the nature of the test, they are rapid, needing just minutes instead of hours.
we are familiar with antibody testing, as many laboratory tests are based on them... pregnancy test.. typhoid test.. hepatitis test.. dengue test..
even now,
effectivity of experimental vaccine action is partially dependent on level of antibody induced in the subject's blood.
"rapid test" used to be antibody test only, because the gold-standard traditional PCR test is slow.
but there are now "rapid PCR tests" in the pipeline.
we have but to ask, what it is we are getting.
btw,
"RT-PCR" does not mean rapid test PCR. RT-PCR still is the traditional PCR we read about. it means, "Reverse Transcription PCR", which is just a lengthier, more descriptive name of what the test is all about.
so,
why is there confusion between antibodies, antigens, and the presence of disease?
ganito yan.
antigen is the microbe itself, virus or bacterium, or parts of it.
a positive result means that the virus or bacterium, or parts of it, is still in the body.
normally, this means, active disease. "may sakit kah, at nakakahawa kah."
if the antibody test is done and it is reactive ("positive"),
it means the body has antibodies, because it has been exposed to the virus or bacterium. remember also, that vaccination can give the same result.
hindi nakakahawa kung antibodies lang.
problems in patient status (not infected, infected, recovered) arise because:
1. there is a time lag between infection, recovery, and antibody level;
2. antigen-antibody curves can overlap, providing no 100% clear delineation among the patient statuses.
in a study done by the pgh folks,
it showed that the predictive value of antibody testing for the presence of the virus, is a measely 20%.
to re-iterate,
a positive or negative antibody test result should not be equated with absence or presence of the virus.Last edited by dr. d; October 21st, 2020 at 12:04 PM.
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October 21st, 2020 12:07 PM #18603
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October 21st, 2020 12:15 PM #18604
Deestone,
antibodies are produced by the body to fight the virus
kaya ginamit ang antibody test to see if you're infected -- IGM = infected, still fighting
IGG = finished fighting
ang problema kasi pag newly infected ka di agad meron antibodies
it takes days to develop IGM so madami false negative (wala antibodies pero may virus)
so ngayon mas prefer ang antigen test coz it detects the virus directly
ang problema naman sa rapid antigen test di sya kasing sensitive ng PCR so if you have low level of virus maari di madetect ng rapid antigen test
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October 21st, 2020 12:18 PM #18605
also nakakainis din ung positive ka sa IGG tapos i-quarantine ka and ipa-swab test pa (PCR)
eh IGG na nga magaling ka na dapat di ka na i-quarantine and di na kailangan i-swab di ka na nakakahawa
kaya fallen out of favor ang rapid antibody test
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October 21st, 2020 12:19 PM #18606
PH active cases looks like it got zapped compared to other active chart...
Last edited by Monseratto; October 21st, 2020 at 01:07 PM.
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October 21st, 2020 12:33 PM #18607here's a thought.
are all antibodies, protective? what if the antibodies are mere marker antibodies?
do all covid patients develop antibodies?
covid is a novel disease.
more research needed...
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October 21st, 2020 01:05 PM #18608
Hmmm, China and Brazil in the same sentence and together on the results of the trials somehow does not give me confidence on the efficacy of the vaccine
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October 21st, 2020 01:13 PM #18610
Kwento ng katrabaho ko, meron daw sya officemate dati na Italiano na tinanong daw bakit...
Traffic!