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What's the difference between a PCR and antigen COVID-19 test?

12 Comments
By Nathaniel Hafer

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Before traveling here in the States, some carriers require a covid test within two days of departure, which means that the highly reliable PCR test is out of the question. Have had several less reliable antigen tests, all negative, but am always wondering if I will be denied travel due to a false positive on that test.

1 ( +1 / -0 )

Well, one of the differences is that the scientist who developed the PCR test has publically and on record stated that the PCR test is not for use on humans. Without getting too technical, the test can find covid in about anything tested. Eg., fruit for example. It is well known that you can test a person several times and end up with different results each time.

3 ( +9 / -6 )

Well, one of the differences is that the scientist who developed the PCR test has publically and on record stated that the PCR test is not for use on humans.

He also publicly and on record said that HIV had nothing to do with AIDS, he was completely wrong on both accounts. In science credentials never replace evidence, if any scientists is saying something without having the evidence to support it (as he does) that has no value and can be ignored.

ho developed the PCR test has publically and on record stated that the PCR test is not for use on humans. Without getting too technical, the test can find covid in about anything tested. Eg., fruit for example.

For a validated test done as instructed this is completely false, the specificity value is precisely something that is calculated based on the lack of false positives, which for most tests used on the developed world is above 99.9%.

 It is well known that you can test a person several times and end up with different results each time.

If the person is close to the limit of detection that is normal, the positive results are true positives and the negative ones would be false negatives because the amount of virus present is barely enough to be detected so sometimes it will not. That happens with all kinds of tests.

-5 ( +5 / -10 )

Being just a layman, I found the article quite informative and easy to understand.

3 ( +3 / -0 )

Apparently, the writer, an expert, is unaware (or deliberately omitting) of the fact that PCR tests have also produced no small number of false-positive results.

1 ( +5 / -4 )

Apparently, the writer, an expert, is unaware (or deliberately omitting) of the fact that PCR tests have also produced no small number of false-positive results

Anything done millions of times will, that reduces in absolutely nothing its usefulness. if the false positives are in the order of one every several thousands tests that still means it is a very precise tool. Also the writer did not omit that the tests have false positives it is clearly written as "With accuracy that approaches 100%, it is the gold standard for diagnosing SARS–CoV–2."

-4 ( +0 / -4 )

Antigen tests do have some drawbacks. Depending on the situation, they can be less accurate than PCR tests. When a person is symptomatic or has a lot of virus in their system, antigen tests are very accurate.

....and if you are not symptomatic and have very little virus in your system, are you considered sick at all? I do not know of any other infection where that is claimed.

1 ( +2 / -1 )

I wish they would use the saliva tests in Japan. That nasal swab is the most uncomfortable non-pain thing I've ever felt.

1 ( +1 / -0 )

garypenNov. 13  11:06 pm JST

I wish they would use the saliva tests in Japan. That nasal swab is the most uncomfortable non-pain thing I've ever felt.

They do, when you arrive back in Japan from overseas.

0 ( +1 / -1 )

....and if you are not symptomatic and have very little virus in your system, are you considered sick at all? I do not know of any other infection where that is claimed

That does not apply for COVID either, asymptomatic people are considered infected (and depending on the titers and progression) can be considered a risk for propagation. In short tests detect infection, medical consultation detect disease.

0 ( +1 / -1 )

I wish they would use the saliva tests in Japan. That nasal swab is the most uncomfortable non-pain thing I've ever felt.

They do, when you arrive back in Japan from overseas.

I wish they implemented it at my local hospital!

0 ( +0 / -0 )

garypen

I wish they would use the saliva tests in Japan. That nasal swab is the most uncomfortable non-pain thing I've ever felt.

Actually, I want to amend that statement. It's the 2nd most uncomfortable thing. The 1st one involved a catheter.

0 ( +0 / -0 )

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