Covid-Test RT-PCR same as PCR?

[daviddunham]

(Question in the title)

 

I did a (free in my country) covid-test because "why not"....

 

To fly to Thailand the embassies state I need a "RT-PCR" Test.

On my certificate it only says "PCR" as shown in the screenshot. Is that the same or will they deny me entry with that?

 

 

[HeijoshinCool]

.

RT designates using Reverse Transcriptase enzyme to change a RNA to DNA.

 

Don't know what they'll say. The only PCR used for COVID is RT, so it should be okay, unless Mr. Murphy gets involved.

[partington]

To confirm above, since SARS CoV-2 is an RNA virus, the RNA must be converted to DNA before PCR can be run, so ALL PCR tests for this virus are RT-PCR tests, whether that is mentioned or not.

[Kiujunn]

All PCR tests for this virus are RT-PCR tests.

They are real-time reverse transcriptase PCR tests. 

By RT, most people mean reverse transcriptase,  and a real-time RT-PCR test may be called rRT-PCR.

Some people may tell you that RT stands for real-time. Doesn't matter,  it's all the same: a real-time reverse transcriptase PCR.

BTW real-time means that the fluorescent marker is added into the same vessel as the ingredients for the PCR and the fluorescence can be watched during the reaction (the R in PCR means reaction)

 

[durhamboy]

Thanks for that Kiujunn. I got really confused with the RT seemingly having 2 definitions. It's good to know that Thailand will accept any test as long as it's PCR. By the way, that rules out some tests for entry to Thailand e.g. the new fast one at Heathrow as they are not PCR.

[ukrules]

15 minutes ago, durhamboy said:

Thanks for that Kiujunn. I got really confused with the RT seemingly having 2 definitions. It's good to know that Thailand will accept any test as long as it's PCR. By the way, that rules out some tests for entry to Thailand e.g. the new fast one at Heathrow as they are not PCR.

I guess you just need to hope the clerk at the check in desk knows all of the above information.

[rabas]

The test result says RNA (PCR) but only (PCR) is highlighted in red.

 

Since RT-PCR is a technique combining reverse transcription of RNA into DNA followed by the PCR amplification step, I expect RNA (PCR) has a similar meaning to RT-PCR.

 

There are several two-step RT-PCR test kits with names like   RNA PCR Kit (AMV) Version 3.0 

https://www.takarabio.com/products/cdna-synthesis/cdna-synthesis-kits/standard-rt-pcr

 

same-same in Thai?

[Kiujunn]

1 hour ago, rabas said:

The test result says RNA (PCR) but only (PCR) is highlighted in red.

It means: "the material has been examined for the presence of RNA of Coronavirus  SARS-CoV2. This examination was done by PCR."

 

As explained above,  this PCR was a RT-PCR.

 

The highlighting was done by OP, I guess.

[John CS]

Anybody want to enlighten people on the % false positives associated with these tests and if the test actually identifies the virus?

[RichCor]

3 hours ago, John CS said:

Anybody want to enlighten people on the % false positives associated with these tests and if the test actually identifies the virus?

Talk to Elon

 

Musk questions coronavirus tests, saying they gave opposite results on same day
By Reuters Staff | 2 MIN READ

 

Tesla’s Musk Says He May Have Covid-19, Calls Tests ‘Extremely Bogus’
Bloomberg press | Stefan Nicola and Tim Loh | November 13, 2020

[partington]

8 hours ago, John CS said:

Anybody want to enlighten people on the % false positives associated with these tests and if the test actually identifies the virus?

Number of false positives depends on the exact test used , but will be extremely low.

 

Negative controls (samples known to not contain the virus) are always run with the tests and if something has gone wrong will show a positive and results of all in the run will be discarded.

 

The test identifies the virus specifically because it is based on two primers which contain nucleic acid sequences unique to that virus alone, and will be chosen for their uniqueness.

 

An objective observer would not trust much of what Elon Musk says given his past utterances and behaviour. 

[RichCor]

1 hour ago, partington said:

An objective observer would not trust much of what Elon Musk says given his past utterances and behaviour. 

While I think Elon is an untrustworthy SOB, and he's as stupid about Covid-19 and it's implications as another orange Tweeting twerp, in this instance Elon is stating what he encountered, feeling unwell and suspected having covid so requested medical staff do a few tests. 2 quicktests came back negative while another 2 quicktest came back positive. all given on the same day by the same staff.

 

That's all his talking point is about        ...how is someone supposed to trust these tests with that outcome?  He also had the standard 24-hour test and is awaiting results. Hopefully he did multiple of those as well. Elon's still an untrustworthy SOB, but I'm interested in the outcome of the information and its implications.

[partington]

Unwillingly I looked at one of these links.

 

It's very clear that he was talking about antigen tests. These are not PCR tests, they are completely different.

 

They are tests for antibodies, that is tests which show you have had the disease for some time and may  even have recovered from it weeks previously. You only develop antibodies many days after you are infected and continue to have antibodies in your blood  for months after recovering.

 

There is no discepancy here at all. PCR tests will show infection way before any antibodies have had a chance to be expressed.

 

Antibody tests, especially rapid ones have very varying degrees of reliability, and are an order of magnitude less reliable than PCR. The UK government has paid millions for antibody rapid tests that have been shoen not to work properly.

[partington]

The edit function seems to have completely disappeared from the site so I can't correct the typos-sorry.

 

[partington]

And of course I read the link too quickly - the tests are NOT for antibodies against the SARs CoV-2 virus  in the blood, as I mistakenly stated, but USE antibodies to detect SARS  CoV-2 proteins in the sample.

 

However the same caveats apply: they are far less sensitive and reliable that PCR tests, and can only detect huge amounts of virus compared to the much more sensitive PCR tests. It isn't surprising that they are not particularly reliable.

[John CS]

15 hours ago, partington said:

Number of false positives depends on the exact test used , but will be extremely low.

 

Negative controls (samples known to not contain the virus) are always run with the tests and if something has gone wrong will show a positive and results of all in the run will be discarded.

 

The test identifies the virus specifically because it is based on two primers which contain nucleic acid sequences unique to that virus alone, and will be chosen for their uniqueness.

 

An objective observer would not trust much of what Elon Musk says given his past utterances and behaviour. 

Thanks for that, I hear a lot about false positives in these tests & that the length or size of the sequence is quite small compared to overall length of the sequence?

I also hear because of PCR cycle of 40+ this picks up remnants of old infections of flu?

Any truth in these statements?

[Kiujunn]

19 hours ago, John CS said:

Thanks for that, I hear a lot about false positives in these tests & that the length or size of the sequence is quite small compared to overall length of the sequence?

I also hear because of PCR cycle of 40+ this picks up remnants of old infections of flu?

Any truth in these statements?

No.

 

The length of the sequence used in the tests is quite small compared to overall length of the virus genome but it is specific to this virus only. 

It's not the length of the tested sequence which is important,  it's the fact that this sequence is unique and occurs only in SARS-CoV2.

 

40+ cycles are not used,  and wouldn't confuse SARS-CoV2  with Influenza anyway, even both are a virus. 

This is like saying,  if you test long enough you might confuse an elephant with a mosquito (both are animals). It's not going to happen,  it's 2 different things. Not all animals are equal,  and not all viruses are equal.

 

 

[treetops]

On 11/13/2020 at 6:31 AM, John CS said:

Anybody want to enlighten people on the % false positives associated with these tests and if the test actually identifies the virus?

False positives in the UK are estimated to be between 0.8% and 4% according to a recent article in The Lancet, a figure described as "a significant proportion".

[partington]

On 11/15/2020 at 3:23 AM, treetops said:

False positives in the UK are estimated to be between 0.8% and 4% according to a recent article in The Lancet, a figure described as "a significant proportion".

It's important to point out that the actual figures are unknown -  these estimates are guesses,  varying over a fivefold range!

 

Actual quote from the Lancet article [my emphasis]: https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30453-7/fulltext

"The current rate of operational false-positive swab tests in the UK is unknown; preliminary estimates show it could be somewhere between 0·8% and 4·0%."

 

A false positive incidence of 0.8% makes the tests 99.2% accurate and of 4%,  96% accurate, so if these figures are even close to being correct the PCR tests look quite reliable.

[treetops]

17 hours ago, partington said:

A false positive incidence of 0.8% makes the tests 99.2% accurate and of 4%,  96% accurate, so if these figures are even close to being correct the PCR tests look quite reliable.

Your figures are incorrect as they only subtract potential false positives from 100% when there are other potential outcomes such as false negatives or inconclusive.

 

It may be the best test we've got, but when The Lancet report describes this as potentially "adversely affecting the positive predictive value of the test" then it has to raise some doubts and cannot be termed reliable enough IMO.