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Lateral Flow Test and Omicron
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By *rFunBoy OP Man
over a year ago
Longridge |
From people I know testing positive for COVID and observations of the Lateral Flow Test they took.
Seems the Omicron variant may turn the Test marker positive very quickly, almost as soon as it hits the 'C' marker on the Tests display.
It normally takes a few minutes for the Positive marker to change but seems since Omicron showed its face, it might be reacting quicker.
A number of friends and colleagues working in hospitals have seen this and although not had sequencing confirmation, it is likely a quick developing Test is might be an indicator of having Omicron variant.
There is nothing scientific behind this but many I have heard of testing positive have said they were surprised at the almost instant result once the solution travelled through into test markers and had not seen it prior to this variant being around. |
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By *rFunBoy OP Man
over a year ago
Longridge |
Might be better tests.
Just comments I've heard when others I know have caught it a second or third time that the tests took longer to develop first time round.
Thinking more, the early tests needed 10 or so drops adding to the mixer prior to squirting onto the pad. Versions today are pre-measured and have a lot more fluid so it could be travelling quicker over the plate. |
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I've used lateral flow tests for disease detection (various diseases) for over 15 years & in most cases a positive is indicated instantly - as soon as that buffer solution spreads across the paper you'll get 1 (or 2) blue lines show up immediately - the 20/30 minute wait time is a contingency as very occasionally one will take it's time & leave you in suspense.... |
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I doubt it's anything to do with the variant and perhaps more the viral load. I watched our son's LFT go positive in July (probably Delta) and that was almost instantaneous with a very dark band at the positive test mark. In contrast, a colleague who tested positive in early December showed me a picture of his LFT, which was quite pale at the positive line. The difference? My colleague was triple vaccinated but at the time, my (18yo) son hadn't had the vaccine. Someone unvaccinated is more likely to have a higher viral load than someone who had 3 vaccines. |
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By (user no longer on site)
over a year ago
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"I doubt it's anything to do with the variant and perhaps more the viral load. I watched our son's LFT go positive in July (probably Delta) and that was almost instantaneous with a very dark band at the positive test mark. In contrast, a colleague who tested positive in early December showed me a picture of his LFT, which was quite pale at the positive line. The difference? My colleague was triple vaccinated but at the time, my (18yo) son hadn't had the vaccine. Someone unvaccinated is more likely to have a higher viral load than someone who had 3 vaccines. "
Intresting! Mine was a faint line too. |
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By (user no longer on site)
over a year ago
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It's nothing to do with varients.
The result will almost ways be instant.
This waiting 20 minutes is complete bullshit - as soon as the control line appears the test is complete. Rapid testing at hospitals and airports do not wait longer than that. |
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By *rFunBoy OP Man
over a year ago
Longridge |
Gladly, I've not yet seen one change state other than the Control.
Just heard others in the NHS commenting on the speed of change. The very first kits on trial with NHS staff had very little fluid added to the mix pot.
Higher viral content does make more sense.. |
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Further, admittedly anecdotal evidence to add. My brother tested positive today, 4 days after his wife first tested positive. He had 3 vaccines. The "positive" test line is extremely faint but definitely there. Compared to the unvaccinated positive test that our son produced back in early July, my brother's did require careful examination to confirm that the line was there. One of his daughters (7) also produced a positive test today with a stronger positive line, she is obviously unvaccinated. A second daughter (nearly 9) remains negative on LFT.
It's an interesting epidemiological study in the family  |
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By *rHotNottsMan
over a year ago
Dubai & Nottingham |
"Further, admittedly anecdotal evidence to add. My brother tested positive today, 4 days after his wife first tested positive. He had 3 vaccines. The "positive" test line is extremely faint but definitely there. Compared to the unvaccinated positive test that our son produced back in early July, my brother's did require careful examination to confirm that the line was there. One of his daughters (7) also produced a positive test today with a stronger positive line, she is obviously unvaccinated. A second daughter (nearly 9) remains negative on LFT.
It's an interesting epidemiological study in the family "
Feint lines right at the start and right at the end when antibodies are lowest. Or could be a sign of just very low antibodies / mild infection, I’m just guessing ! |
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By *rFunBoy OP Man
over a year ago
Longridge |
Just Googled and this has started appearing in the press:
Doctor shares warning over faint lines on Covid tests - and what they could mean.
Dr Nathan Hudson-Peacock says there is a testing 'interpretation window' of usually 30 minutes, but leaflets that come with the kits should be double-checked to make sure to make sure.
A line next to the 'C' means the test has worked, as the C stands for 'control', but a line next to the 'T' (test) indicates a positive Covid reading.
Dr Nathan Hudson-Peacock told ChronicleLive "Essentially, if *any* line appears before the end of the interpretation window this is a *positive* test and you must isolate and book a PCR.
However, if a line appears *after* the interpretation window then this does not count as a positive test. You do not need to isolate and you do not need to book a PCR."
There us also more about low level virus load.
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"Further, admittedly anecdotal evidence to add. My brother tested positive today, 4 days after his wife first tested positive. He had 3 vaccines. The "positive" test line is extremely faint but definitely there. Compared to the unvaccinated positive test that our son produced back in early July, my brother's did require careful examination to confirm that the line was there. One of his daughters (7) also produced a positive test today with a stronger positive line, she is obviously unvaccinated. A second daughter (nearly 9) remains negative on LFT.
It's an interesting epidemiological study in the family
Feint lines right at the start and right at the end when antibodies are lowest. Or could be a sign of just very low antibodies / mild infection, I’m just guessing ! "
The antigen tests (LFTs) detect the S protein antigen. The tests work like a pregnancy test basically, same idea. The test paper for COVID LFTs is impregnated (pun not intended) with antibodies against the S protein. If a sample containing the S protein (so COVID positive) passes over the impregnated area, the S protein binds to the antibodies, they aggregate and a change in colour is detected at this point.
Pregnancy tests work exactly the same way, except that the antibodies impregnated on the test strip are against human chorionic gonadotropin hormone, which is high in pregnant women.
For the COVID test strip to show a feint line, there must be a comparatively small amount of S protein in the sample, which would correlate with reduced viral load.
However, there's always the possibility that LFTs designed with the "original" S protein antibodies are less effective at binding to Omicron S protein due to the mutations and that the feint line is just a feature of Omicron. It does concern me that people may have feint or apparently negative tests and still have Omicron. My PT is a prime example. His girlfriend got a positive LFT on Christmas Eve. He had some possible symptoms yesterday, but produced several negative LFTs. He's isolating anyway out of a sense of obligation. Ditto a work colleague who had symptoms, tested negative for three days on LFT but positive on PCR and definitely had COVID. He eventually got a positive out of an LFT on about day 5 of symptoms.
I'm not convinced by LFTs in their current design for Omicron. |
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By (user no longer on site)
over a year ago
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The antigen tests (LFTs) detect the S protein antigen. The tests work like a pregnancy test basically, same idea. The test paper for COVID LFTs is impregnated (pun not intended) with antibodies against the S protein. If a sample containing the S protein (so COVID positive) passes over the impregnated area, the S protein binds to the antibodies, they aggregate and a change in colour is detected at this point.
Pregnancy tests work exactly the same way, except that the antibodies impregnated on the test strip are against human chorionic gonadotropin hormone, which is high in pregnant women.
For the COVID test strip to show a feint line, there must be a comparatively small amount of S protein in the sample, which would correlate with reduced viral load.
However, there's always the possibility that LFTs designed with the "original" S protein antibodies are less effective at binding to Omicron S protein due to the mutations and that the feint line is just a feature of Omicron. It does concern me that people may have feint or apparently negative tests and still have Omicron. My PT is a prime example. His girlfriend got a positive LFT on Christmas Eve. He had some possible symptoms yesterday, but produced several negative LFTs. He's isolating anyway out of a sense of obligation. Ditto a work colleague who had symptoms, tested negative for three days on LFT but positive on PCR and definitely had COVID. He eventually got a positive out of an LFT on about day 5 of symptoms.
I'm not convinced by LFTs in their current design for Omicron. "
Lateral flows are anti-nucleocapsid so aren't influenced by S variants.
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By *rHotNottsMan
over a year ago
Dubai & Nottingham |
"PS: I am not referring to feint lines that appeared outside the testing period. These appeared within moments of the test being carried out, so are valid results. "
Yes that seems very common , I’m my experience, people I know and myself it was at the start and end of infection |
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By (user no longer on site)
over a year ago
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"I’m pissed off cos we can’t get lateral flow tests anywhere"
I couldn't get any for a while and could get any online.
I managed to order some the other day though they haven't arrived yet.
Check online several times A-day because they do become available you've just got to be quick |
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By (user no longer on site)
over a year ago
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"Will keep trying
Just think they handy to have
My son has just for covid and we can’t test as don’t have any"
Might be worth booking in for a PCR just to be sure. |
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By *rFunBoy OP Man
over a year ago
Longridge |
"I’m pissed off cos we can’t get lateral flow tests anywhere"
Have you tried ordering for delivery via mail?
I though that S Gene missing in a PCR test was an indication of Omicron variant? Omicron still shows on a LFT. |
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"I’m pissed off cos we can’t get lateral flow tests anywhere
Have you tried ordering for delivery via mail?
I though that S Gene missing in a PCR test was an indication of Omicron variant? Omicron still shows on a LFT."
Someone above has corrected me. The LFTs use the anti-nucelocapsid antibody. Not the S protein. So mutations in S shouldn't have any impact.
It would appear to be a viral load issue with feint vs bold results on the strip. Makes sense. |
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"Sure does..
Would be curious to see if a lighter marker ended up a milder or asymptomatic outcome, and a darker became heavier symptoms.."
Our family/friends anecdotal evidence = lighter line correlates with few/no symptoms. Heavier line = more symptoms/more unwell. |
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By (user no longer on site)
over a year ago
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"
I though that S Gene missing in a PCR test was an indication of Omicron variant? Omicron still shows on a LFT."
S gene drop-out on qPCR can indicate omicron but just to clarify the virus still has spike protein. The drop out is due to mutation(s) at probe annealing site. Would still need to be sequenced to confirm. |
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By *aseMan
over a year ago
Gourock |
"From people I know testing positive for COVID and observations of the Lateral Flow Test they took.
Seems the Omicron variant may turn the Test marker positive very quickly, almost as soon as it hits the 'C' marker on the Tests display.
It normally takes a few minutes for the Positive marker to change but seems since Omicron showed its face, it might be reacting quicker.
A number of friends and colleagues working in hospitals have seen this and although not had sequencing confirmation, it is likely a quick developing Test is might be an indicator of having Omicron variant.
There is nothing scientific behind this but many I have heard of testing positive have said they were surprised at the almost instant result once the solution travelled through into test markers and had not seen it prior to this variant being around."
Aye  |
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By *alcon43Woman
over a year ago
Paisley |
"From people I know testing positive for COVID and observations of the Lateral Flow Test they took.
Seems the Omicron variant may turn the Test marker positive very quickly, almost as soon as it hits the 'C' marker on the Tests display.
It normally takes a few minutes for the Positive marker to change but seems since Omicron showed its face, it might be reacting quicker.
A number of friends and colleagues working in hospitals have seen this and although not had sequencing confirmation, it is likely a quick developing Test is might be an indicator of having Omicron variant.
There is nothing scientific behind this but many I have heard of testing positive have said they were surprised at the almost instant result once the solution travelled through into test markers and had not seen it prior to this variant being around."
I had three negative LFTs last week and had a positive PCR. The Omicron variant is taking longer to show symptoms and on LFTs as far as I’m concerned. No one else in my house has tested positive. I’ve been in bed since Christmas Eve. It’s definitely worse than a mild cold. |
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By *rFunBoy OP Man
over a year ago
Longridge |
Hope your well soon Falcon xx
Just spoken to friend who has colleague who was feeling rough, taken three LFT's over 2 days all showing -ve so went for PCR yesterday, that's come back +ve.
She's retaken an LFT out of curiosity and this one showed +ve. Timing and lag seems to be going on but strangely, isolation days seem to be getting shorter..
Hopefully, the point at which you are most infectious follows this as they worked together a few nights ago. |
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