How SARS-CoV2 Antigen Rapid Tests work (Covid-19 Testing)
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- Опубликовано: 3 дек 2020
- Hey Friends,
Covid19 requires a lot of testing. This cannot be done by PCR alone since the time effort would be too much and lab capacities are already exhausted.
With antigen rapid tests (mostly lateral flow tests) the result is shown within 15-30 minutes. This can revolutionise testing! Today, I am going to explain how these antibody-based tests work. The principle is similar to an ELISA.
If you have not checked out how an ELISA works, click here:
• ELISA (Enzyme-linked I...
Thanks for watching!
Cheers
Henrik 
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I very much appreciated this simple explanation, as well as your interaction with viewers questions. From a COVID patient, thank you!
Thanks heaps for this post. Helps me to clear doubts about whether I didnt wait long enough or had missed it.
Thank you!! Thank you for explaining. I'm taking a test like this now and read ALL of the directions and none of the directions explained how to read the test results. Thanks so much. Super helpful!
A PCR test does not detect viruses directly. Rather it identifies fragments of genetic material which could either come from a living or dead virus. In order to aid detection, the test works by amplifying the genetic material in a sample through multiple cycles.
Thank you! For explaining antigen test in a simplest way.
Really simple breakdown. I appreciated this explanation.
the best explanation of how a RTK works! thanks a lot buddy
Thank you! a very simple and effective explaining illustrations :)
This was the best explanation I’ve seen. Thanks!
Thank you! for explaining this to me in how it works it was a great help.
Amazing explanation thank you! Yours combined with Wired's, clears it all up
Interesting and clear scientific explanation of how these tests work: the secondary line acts to capture a few antibodies, whether or not they bound to the targeted virus, allowing the capture of antibodies in the first line to signal that the specific antigen is present
Thanks dear
I'm gonna buy a test kit and your video makes it the simplest way
Bless you
Fantastic explanation! I absolutely adore this
Thanks, quick and clear!
Clear explanation. Thank you!
Very informative, thank you for the information
Excellent explanation, concise and clear. Thaks you so much!
Thanks, very informative and easy to understand :-)
Vielen Dank fürs Video! Sehr hilfreiche Erklärung!
This was great. Thanks.
Nice! what I'm doing is similar to this, testing food hazards using fast, simple, integrated smart devices!
Excellent explanation!
Hello, thank you for providing such a great explanation video about how antigen rapid tests work. Because of that, may I ask you would it be okay if I take a few screenshots of this video as to use them when I explain about lateral flow essay?
Really appreciable
Amazing job.
You are perfect thanks 😊
I tested today, It shows red on C line after few seconds It said negative for some times. And then after few min, the very faint T line appear slowly. And it is showing positive. Why does the C line appear red for the first and T line appear after few minutes?
Thanks for this. It's fascinating.
Thank you ✨🙏
Thank you 👍
that's the best! thanks
Hey Henrik, i did a test on myself yesterday. It was negative. However today i can see a dim test line. I know you can only read till 30 minutes after the test. But is there an explanation on how the test line only show up now? Should i redo my test?
Hey Robbe, first: I would recommend to redo the test today, yes. As you´ve already said, just read it out in the specific time-window. Look very carefully this time again.
I have experienced a test line long time after the readout myself for some tests.. so I would not worry.
The reason why that happens? Honestly, I don´t know.
Hello, i am doing an assay of point of care tests and was just wondering which surface marker of the virus does the first line of antibodies bind to
Thanks for sharing your video, God bless.
Amazing
Great vid. My only question is why do we need a secondary antibody line aka control line if the primary immobile antibody is enough to indicate the presence of the viral protein?
you need that second control line to tell you if a negative result was successful.
someone might have put in too little sample for the capillary action to occur fully. maybe the sample did not reach the first control line at all. that is why you need the second control line to tell you if the sample reached the first one so you know that a negative result is successful
Hey Henrik. Great explanation, thank you. I recently tested positive for Covid and I am very close to finishing my self isolation. I have taken an antigen test today and the test line if very faint. If the test line is extremely faint what does this mean?
Still positive. There must be no line
In our case (3 members of my family), a faint line was a halfway point between positive and negative as we always recorded a negative test the following day. Perhaps you also tested negative the following day?. Alternatively, it may be unique to the brand of test we are using
My dad is a doctor and says if it’s faint you are either in the beginning or final stages of covid. I reckon it’s to do with the abundance of the virus that’s in the body at the time of testing.
@@bitz3225 Absolutely correct!
@@bitz3225 yes, I believe your dad :) My wife took 2 tests. The first one, the line was fain. She took another one the next day and it was positive. That same day she went to get the PCR test done and 3 days later the results were "inconclusive" SMH
this test is so genius
Yeah i did a test a couple of days ago it was an extremely faint red line but it was positive that was on Saturday i believe but i felt ill maybe a day before i tested positive. I feel fine now i don't have symptoms i haven't done a test since Saturday though.
Great that you feel fine!
Great videos. I was wondering what program you used to make these animations?
Thanks, honestly it is still powerpoint.. :D
@@henrikslab Hi sir, I tested covid 2 months ago with some symptoms like feeling weak, the next day after that I sneeze a lot (I have nose problem but that day I sneeze a lot more than usual), it got 2 very faint lines after 1 min, but the T line then slowly faded and disappear after 15 mins. I rested, take care of myself and sleep a lot and the next day I was completely normal. So I’m very wonder if I had covid or not? I hope you can help me, thank you (I’m not a native english speaker so my english is pretty bad)
@@ghxbn7389 Hey thanks for reaching out! Even with a faint band it is rather likely that you had the virus! There is a slim chance of a false positive test, but it is more likely that you had it and you had a very mild case.
Still don’t understand when binding means and I gold is important
So when getting an antigen test for travelling , how is it determined that a person is safe to enter that country? The test should be positive or negative?
the test should be negative
Question: What if you put in blood as a sample instead?
why do we need to wait 15 minutes for results even if the control line is visible?
Because in some cases, the test line can appear minutes after the control line is there (I have seen it multiple times myself when working in a test center)
@@henrikslabtrue, whereas the thumbnail to this video upload reads positive, since both lines are visible, or if just the Control line reacts, then that would read negative.
Hi, I did a test just know. But the line of T was showing first. Then C come out later. It is positive?
Yes, that is positive. Stay home and safe!
Can I ask why the second line on T isn't like visible or highlited but can be seen if looked very closely or if light is shined on it?
Sure, this not the case for all antigen rapid tests, but I have seen it for some companies, too! Honestly, it shouldn´t be visible to prevent confusion
How one line color but another line is blur what it's that mean?
Are you positive if there’s a line when the open the test up?
Would an extremely faint line, one you can only see at certain angles/lighting mean a positive result? Took a PCR to confirm regardless but curious on this.
Yes, extremely faint is still considered positive, but it´s totally correct to confirm this with a PCR test. Well done!
Does the test strip contain covid antibodies ? are these antibodies made synthetically ? is the test strip made with actual covid particles ?
The test stip is NOT made with any covid virus parts! On the test there are antibodies AGAINST covid virus parts.
If one t line is coming very dim red that it is hardly seen what does it mean
It is also considered positive in this case (even very dim test lines)
Hi, what if the line is extremely faint, i can barely see it but i think it is there. Am i positive or not?
Faint line plus control line signals positive
Hi Henrik,
The test-kit instruction say that a viable readout can only be done between 15-20 minutes. Do you know if the line should be visible before the 15 minutes passed and stays visible after 20 minutes?
Hey, hope I get your question right: I myself worked in a study testing different of those test kits... they vary in handling and their reactivity quite much... Most I saw, stayed “positive“ for way more than 20 mins.. however many really turned positive just shortly before the time for readout.
I deeply recommend to do the read out in the time span which is mentioned on the kit!
@@henrikslab thank you for the answer. I work at a university, where students have to self test before entering. Many don't wait the full 15 minutes, but just wait until the first bar is visible. Not surprisingly our positive rate is 0.
If you still have access to the testing facility, do you mind making an example video of a positive corona test?
@@MatthiasPitscher our study closed already in march, but I can make one with a rapid test myself
@@henrikslab that would be great! I just want to see how a positive test looks like over time.
@@MatthiasPitscher Unfortunately, I do not intend to be positive just for testing purposes.. :D
Thanks for the video. I did two tests with same kit and both had only the T line showing Red. C was not showing anything. Not even a feeble line. I did follow the instructions. As per the kit, it is supposed to be invalid. But your video shows that T line bright's up only when there is an infection, so not sure why this is to be treated as invalid. Whats the relevance on C if T itself looks to be sufficient to say if the test is positive.
You are absolutely correct! Your test is indeed invalid.. The control line should be visible in any case, otherwise something is wrong or broken with the test.. I recommend to get tested with a test of another brand
you probably didnt get the sample correctly
Thnk you 👍
You´re welcome
Hi, this is a brilliant video. What software did you use to produce it?
Powerpoint
I would love to know where to get these tests... anyone have info on them??
Where are you living? In Germany they are sold by pharmacies and even in super markets now
Hi Cindy, you can contact marina@duxbio.com, we can supply.
Has anyone had a test where the “Test” line is clearly red, but the “Control” line is very faint? Is this considered a positive or is this indicating an invalid test?
It is considered positive!
(A likely explanation: the viral load is extremely high and as shown as in the video, most viral particles bind to the antibodies on the Test line - only the ones that are left, bind to the control line.)
-> again: speculation, but the test is definetely positive!
I had the same thing happen, my RT-PCR test is also positive so yeah it doesn't matter if the C line is dim
the instructions say to read the results between 15 and 30 minutes. Is it usual for the test line to become visible after 15 minutes, while the control line is already visible after a few short moments?
Yes, that is frequent for some tests! There are many different on the market. I was working with some where the test line always showed up way later than the control line.
Most important: Always wait until the time (written in the manual) is over!
Yes, that is frequent for some tests! There are many different on the market. I was working with some where the test line always showed up way later than the control line.
Most important: Always wait until the time (written in the manual) is over!
And where is graphine oxide? On the tip of the swab..or??
Hi, i just did my rat test, and is result the test line is dark and visible but the c line is visible but not dark.
What is it mean
That means much virus, you have Covid19 (you are positive). Get well soon! :)
Hey, thanks for the info., I actually wanted to ask that I did a rapid test yesterday, it came out as (non infective)...I don't know if that means positive or negative, Please tell me what does it mean?
Could you send me the name of the test/kit?
I actually assume that "non infective" should mean negative, but just to be 100% sure, it would help to read the manufacturers handbook
nice
can I ask i got an antigen and its T is with line and the C is grayed out
Greyed out is considered like a thin line. The test is positive!
what if both lines appear 1 min after doing it?
In this case you are also positive, but make sure to always check the result after the time recommended by the test kit
My mom says i tested negative but the thing shows a pink reddish C line and a blackish or faint T line. Can you explain?
This is clearly positive.
Mine gave my positive in like 30seconds
So if I have a sinus infection, flu, or covid it won't get detected
I mean it is a rapid test for SARS-CoV-2 (Covid)... so if you have Covid this should be detected in the optimal case! But Flu or another infection will not be detected, yes!
hi henrik!
if you would like, can you explain why these tests sometimes cause false negatives or false positive?
thanks!
Hey Jessica,
False negatives are way more frequently compared to false positives!
A test can be false negative, when the viral load (amount of virus) is not so high (e.g. at the beginning of an infection or the last days after the infection)
What if it takes longer than 15 minutes to form the second line, is the result still positive?
It depends on the instructions of the test kit. If it clearly states you should read out the result after 15min, you should do that. If it has another range, check the result after the time indicated on the test kit. But let me say this, if you see something right after this time, I would advise you to repeat the test and behave if you would have been infected (maybe doing another test the following day). All the best!
The BD Veritor SARS test doesn't offer any information on interpreting their tests. They ask you do use a phone app so they can assess the results. My wife clearly has two two lines, but the BD phone app said her test was negative. Super confused now.
I checked their homepage and also find it a bit confusing...
bdveritor.bd.com/en-us/main/rapid-antigen-testing/covid-19
Be careful for now and repeat a test with a kit from another brand if possible or go to a public test center.
Merry Christmas!
What is the exact output of the device?
+ or - ?
it MIGHT be that the two lines do not indicate positive in this specific test (but not sure either)
@henricks lab. Can you please help me with my question. I took the the antigen saliva test rn. I took 3 actually. Two showed dark red lines at C but very thin, invisible shadow like line at T. The line at T is almost unseeable and you can only notice when u look carefully for it. Does that mean I’m positive or negative. I took a pcr test 4 days ago and was negative.
V
I would recommend to get a PCR test again. Thin red lines at the Test line are also counted as positives... If possible stay safe and home and try to organise a PCR test to make sure! All the best for you!
@@henrikslab I got the nasal test done and it’s negative. Does that mean I’m good?
@@yaqoobrox3537 negative sounds good, yes!
i made 4 ag tests, 2 positive and 2 negative, which one i should believe?
In that case, assume you are positive and organise a PCR test to confirm that.
Q: are there any chemicals on the swab? Or only the chemicals in the tube you put in the first hole? TY
The chemicals are inside the tube (more specifically inside the buffer)
Henrik's Lab - Thank you!
Quick question 🙋
I play around with the art test for fun by putting normal water droplets inside, the result turns out to be positive, why is that so??? Anyone knows??
First of all: It is completely against the instructions and does not prove the test isn´t reliable, but honestly I like your curious thought of testing things and playing around a bit!
I would appreciate a short video, where you show this exactly, would be cool to see, before one responds why that might be :D But I found an interesting paper where they did exactly what you did (again: which is clearly against the instructions in the manual and therefore doesn´t show the test isn´t working):
www.ncbi.nlm.nih.gov/pmc/articles/PMC8372450/
This is a possible explanation in their eyes:
"A likely explanation for the interference could be an altered pH in these solutions, which could modulate the function of the antibodies coated in the test line. An optimal pH, stabilized by the supplied buffer, must be critical for true positivity."
@@henrikslab wow thanks for the reply! I’ll look into it
Edit: yea after looking into it, I believe this should be the best answer. Thanks a lot!
thank you for the explanation and how accurate are these test exactly?
Well, this is actually varying.. some test kits are pretty inaccurate and may not detect the virus if it is not super abundant.. some are better! In general you can say by rule of thumb: they detect 60-90% of PCR positive patients.
Here a study (evaluation of one test) in which I have also contributed:
www.medrxiv.org/content/10.1101/2021.03.02.21252430v1
oh ok thanks
the one i took was approved so thats a good sign
Hi Henrik, I got tested positive today. There were instant 2 lines, I redid and they are the same. I’m also having covid symptoms. Do you think an ordinary cold can come out positive on the test results?
No, ordinary colds won´t be detected by the tests.. So this must be Covid19. Get well soon!
What is the C line is dark and the T line has a faint pink line, like mine does right now?
This is still considered positive, according to the test you carry the virus infection
@@henrikslab You're right. I found out from the Pharmacist and my Dr's receptionist after. I was sick yesterday! Feeling a slight bit better today. The sad thing is I'm going to miss out on a Rod Stewart/Cheap Trick concert I've had tickets for, for 2 years. 😒
Of all the times ive taken tests, todsy is the first I've tested positive lol
Ok but how do you get the sample on? You spit on it?
No, there is a nasal or nasopharyngeal swab...
Watch this video here to see how they do it:
ruclips.net/video/aCLISf3Na58/видео.html
If it was faint C and normal red line in T.
is it also positive?
It is.
@@henrikslab it is invalid. After second test. It’s negative only C Line. These tool is seem to be 50/50 work.
@@henrikslab I think positive is only by C Line is not faint.
C + faint T
C + T
Faint C + T must be include the void invalid result
No C + T
No C No T
Actually, it doesnt matter whether it is faint or not.. your first test is definetely considered positive.
If there is the possibility for you:
Go get a more precise PCR test
Avoid meeting people as long as you know about it
@@henrikslab the first test is after fatigue arrived from city and he test after eating, so the saliva is surely mix up with food.
That’s why he test again in the morning is negative.
Any particular reason it’s called the antigen test and not the virus test?
I did this today and it was negative with a slight red line after 15 minutes but after an hour it's now haves a blue line that's much more transparent than the red line as it still looks the same. Does that me I'm positive?
Quote that an new line appear after an hour so now I have two lines
I read on one of the other comments that they had a similar situation like me so I want to know if I'm good or not cause one of my relatives was tested positive.
@@swagb9149 two lines (no matter how faint/slight) indicate a positive result
Some tests shouldn’t be evaluated after 30 min, because they can be false-positive. I advise you to re-do the test and check the line(s) after exactly 15 min.
Why it's showing t line only?
Don´t know WHY, but in that case, the test is invalid! Take another one
Can it distinguish between SARS-CoV-2 antigens and other common human coronavirus antigens?
Most Antigen Rapid Tests target the Nucleocapsid protein which has a very specific structure. So yes, it can differentiate between those different Coronavirus types.
Some Antigen Tests also use the Spike Protein
pubmed.ncbi.nlm.nih.gov/34037382/
@@henrikslab alright, thanks.
Can you imagine natural selection somehow preventing the COVID virus from sticking to the primary antibodies in these tests?
What if it show 2 lines but one is faded
positive test result
No one talks abt this anymore...they are now talking abt nuclear test!! Stuvi
How do you explain weak lines
Weak lines (at T) are still an indicator of virus material... there are different reasons for that:
-not so much virus material
-swap was not good enough
-test kit is not so sensitive
Does that mean, if the sample is positive, the T line will show up immediately?
No, I have seen it so many times that the T line is getting visible after the C line is already there..
sometimes the T line appeared after 10 mins.. It´s still considered positive then!
Herbs are the best, I got cured completely using DR RORPOPOR HERBAL on RUclips herbs supplements to defeat PCR • his medication is active....... YOU ARE THE BEST
@@henrikslab hi, what if the test line appears immediately? Is it common or could it be a faulty test? Thank you
@@pizzicotta It may point to a high viral load. It is not faulty if the test line appears early
My son's name is Henrik as well
He must be a great guy!
@@henrikslab yes he is 1.4 year old
Has anyone had a test come up
Positive. But when you look at it in the trash later the line has went away??
That can happen. Important for you is to read the test result in the time window written in the instructions
@@henrikslab well what if result is inconclusive in that timeframe?
I have a faint grey line is that positive?
control line and test line? Then: Yes, that is positive
Does the bar code (id number) show the result when scanned?
What do you mean? I don´t understand the question
No, it doesn’t. It only leads to a certificate, that proofes that it is a legit test. The result can only be seen via the 1/2 line(s) on the test.
Do you have Covid even tho the c bar is very visible and the t bar barely visible?
Yes, in this case you have Covid!
@@henrikslab oh thank you
same thing happened to me, wondering if i have covid and how i got covid in the first place lol
I got red line C but mass of red smudge @ T 🤔
Positive result, you got infected. Have a fast recovery!
How does an invalid result work? T line but no C line
Yes that or no line at all
@@henrikslab I mean, how does an invalid result work? The video didn't show how the antibodies would move to create an invalid test. One for just T line and one for no line at all? Does the test know if the swab has actually been used and mixed with the solution that you put droplets onto the test?
am I suppose to put my test in the fridge?
First of all, I assume you talk about storage BEFORE use..
That really depends on the kit (brand and type of rapid test)! You may have a look on the test kit (a recommendation of temperature should be listed on the kit somewhere).
In general to be safe, it shouldn´t be stored to cold but also not too hot (most tests have a range between 4-30°Celsius, but again this is specific - please check in your manual).
So what's the function of second line..
I assume you are talking about the "control line" (C)... This is a good question! The control line is basically present to indicate that the test is valid... in case the control line does not appear at all... you know the test is not valid (it was either performed incorrectly, the test itself had an error or whatever).
@@henrikslab oh got it thank you so much…for clearing doubt
I wonder why this test is names as antigen test if there is not involvement of antigens.
The antigen is the part -here a virus particle- that is recognized by the antibody. So the test uses antibodies to check for the presence of antigens.