Can a COVID test show your level of infectiousness?

Submitted ⁨⁨1⁩ ⁨month⁩ ago⁩ by ⁨Tylerdurdon@lemmy.world⁩ to ⁨[deleted]⁩

I’ve seen many tests (we’re talking the average retail 4-drop kits) come up with varying degrees of positivity as a person goes through a bout with COVID.

Once they test positive, it’s usually coming up with that T indicator long before the C shows to.

However, I’ve noticed that even that length of time for the T to show can vary. Sometimes it starts faded and fills in but sometimes the line can go full color as soon as the liquid hits it. Other times it may take a while and come up after the C (once closer to getting over it).

My thought here is the virus particles per million in a person’s mucus are fluctuating during the course of their sickness and the more virus particles, the faster that bar is going to pop on the COVID test.

So then, is it stupid to think the faster the T shows up, the more infectious a person is with their coughing/sneezing?

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psilotop@lemmy.world ⁨1⁩ ⁨month⁩ ago
Very firmly no. Even PCRs are not useful. People can pull out an example of “my friend infected me when her test said X” but that’s just coincidence. This has been studied extensively during COVID and there is no reliable correlation between test value and infectivity.

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Boozilla@lemmy.world ⁨1⁩ ⁨month⁩ ago
Too many variables. There’s two types of test, antigen and PCR. The chemical reactions in both can be impacted by ambient temperature and humidity, light exposure, air pressure (altitude), air quality (contaminants) and so on. At-home testing is far from lab conditions. False positives and false negatives are possible. I wouldn’t put any stock in the timing.

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bobagem@sh.itjust.works ⁨1⁩ ⁨month⁩ ago
Everyone is saying no, and I’m no expert, and I believe that for purposes beyond amusement value, the answer basically is no, but…

The times that I’ve had covid, the strength of the T signal has started weak, gotten strong, and then trailed slowly off over the course of days.

Same for family members.

Same for acquaintances who I’ve seen post day-by-day test photos on social media.

I’ve read that if you are vaccinated and boosted, your antigen response kicks in faster and so more closely parallels your communicability curve. That is to say that unvaccinated people will be communicable before home antigen tests start noticing that you’re responding. But people who have had covid or vaccinations will test positive sooner. And specifically I’ve read that during the incubation stage when you are infected but not very communicable yet the tests may miss you, but on the other hand that’s okayish because you’re not very communicable yet.

Everything that everyone has said about all the variability can be at least partially controlled, if you are using the same test batch, in the same location, at the same time of day, following the same idiosyncratic procedure for each.
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- tired_n_bored@lemmy.world ⁨1⁩ ⁨month⁩ ago
  This
  
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DrabPoultry@midwest.social ⁨1⁩ ⁨month⁩ ago
A home test won’t. A PCR gives you some idea if you can get them to tell you the CT (cycle threshold) value of your test. The CT value corresponds to how many times the temperature cycled before the amplification signal of the sample became detectable. Lower CT values correspond to higher viral loads.

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- elvith@feddit.org ⁨1⁩ ⁨month⁩ ago
  Even then, the CT roughly indicates the amount of virus that was in the sample - which correlates with how infectious you are. But it also depends on the quality of the sample and how it was taken. If you’re highly infectious but the slab was not correctly inserted, you might have less virus on your sample as one would expect and appear less infectious.
  
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  - DrabPoultry@midwest.social ⁨1⁩ ⁨month⁩ ago
    Definitely. Plus, you can absolutely get different CT values from two different testing platforms. Some PCR tests are more hands-on than others and the result can vary based on the quality of processing and on the settings that are used in the analysis software.
    
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zenharbinger@lemmy.world ⁨1⁩ ⁨month⁩ ago
no

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Oth@lemmy.zip ⁨1⁩ ⁨month⁩ ago
The effect you are describing is “viral load”; the degree to which a virus is present in the body. And while this is an indicator of how infectious you are. It is especially important for people with HIV to see if they are “safe” or need their medication adjusted.

However, an at-home test will not be a good indicator of this. These have too many variables such as the site that was swabbed, time delays from the various biological functions, how well you used the kit and even variability in the kit itself.

To properly test for viral load, a blood test should be used. I worked with a company that tested for viral load via expelled breath, and while this was a good indicator of infectiousness y/n, and was faster than a PCR, it was not more accurate.

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- Tylerdurdon@lemmy.world ⁨1⁩ ⁨month⁩ ago
  Interesting, thank you!
  
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Banichan@dormi.zone ⁨1⁩ ⁨month⁩ ago
nope

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RightHandOfIkaros@lemmy.world ⁨1⁩ ⁨month⁩ ago
AFAIK, no. The tests you can get won’t show exactly how much viral load you have, only that you have enough to trigger the test to return a positive result.

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