COVID Rapid Test sensitivity differences

[Torn Mind]

My most recent COVID experience has led me to use different companies' test products because that's what different companies or governments give out. Kaiser sent me iHealth, the feds Carestart, and the local county, via public libraries, give about Abbott's BinaxNow.

The Abbott Binax product is the one with the most points of failure, but it might be the most sensitive? I mean, having to deposit six drops, and then three rotations(with no markers on the swab) can lead to a mess up somewhere.

If I shine a super bright light on the Abbot test strip, I see a ever-so-faint line, and their manual say that even the faintest of lines still means being positive with COVID. I tested negative yesterday with a different test.

The iHealth test is the most convenient and least able to "screw up' the process, as both the cap and the dropper are securely attached screws, but the paper test strip might be less sensitive.

I also used the CareStart kit, which is likely more prone to spills during the process than the iHealth, as the tube with liquid is sealed only by foil and no cap. I tested negative on the CareStart...or the paper did not preserve what I thought was a very faint line when it was moist.

Rather than take only 5 rotations of the swab, I usually do ten.

I still have some symptoms but it's not much as of today. Yesterday, I had plenty of rough coughing. So it the line indicating positivity would correspond with my current state.

 

[dullard]

<-- Worked on medical devices for years. In the PCR field, but no Covid tests.

There are three main requirements of proper medical device design: effectiveness (i.e. it must do what the product's intended use states), safety, and usability. The usability test was added by the FDA to the requirements a decade or so ago. Meaning that the devices must be tested by various users to show that there are no significant failure points (if directions are followed). There also should be no significant user-to-user differences to be a medical device.

I didn't do a long search for the sensitivity of the devices you listed, but here is a chart of sensitivities of a range of different rapid Covid test strips: https://pubmed.ncbi.nlm.nih.gov/34407759/#&gid=article-figures&pid=fig-5-uid-4
Notice that sensitivity ranged from 37% to 99% depending on the manufacturer (look at the top graph in the image). Thus, to answer your question, yes there are tests that are far more sensitive than others.

The same paper found no significant differences from user-to-user including trained professionals and self-swabbed customers. "Test performance does not appear dependent on the operator." https://pubmed.ncbi.nlm.nih.gov/34407759/
In layman's terms, I bet that the Abbott test probably works with 3 drops or 9 drops, but 6 is the aim. Or the test works with 1 swirl or 5 swirls but 3 is the aim. The tests are not that impacted by minor user errors. The manual will state 6 drops and 3 swirls, but that exact number actually isn't very important.

What is important that should be in the manual (and unfortunately isn't in the manuals that I have read) is that you are trying to get your nose wall cells on the swab. You aren't trying to get snot on the swab. Blow your nose out completely before swabbing. If you are really trying to get the nose lining cells, then you don't need to go 10 revolutions.

 

[Torn Mind]

There are three main requirements of proper medical device design: effectiveness (i.e. it must do what the product's indtended use states), safety, and usability. The usability test was added by the FDA to the requirements a decade or so ago. Meaning that the devices must be tested by various users to show that there is no significant failure points (if directions are followed). There also should be no significant user-to-user differences to be a medical device.

I didn't do a long search for the sensitivity of the devices you listed, but here is a chart of sensitivities of a range of different rapid Covid test strips: https://pubmed.ncbi.nlm.nih.gov/34407759/#&gid=article-figures&pid=fig-5-uid-4
Notice that sensitivity ranged from 37% to 99% depending on the manufacturer (look at the top graph in the image). Thus, to answer your question, yes there are tests that are far more sensitive than others.

The same paper found no significant differences from user-to-user including trained professionals and self-swabbed customers. "Test performance does not appear dependent on the operator." https://pubmed.ncbi.nlm.nih.gov/34407759/
In layman's terms, I bet that the test probably works with 3 drops or 9 drops, but 6 is the aim. Or the test works with 1 swirl or 5 swirls but 3 is the aim. The tests are not that impacted by minor user errors. The manual will state 6 drops and 3 swirls, but that exact number actually isn't very important.

What is important that should be in the manual and isn't is that you are trying to get your nose wall cells on the swab. You aren't trying to get snot on the swab. Blow your nose out completely before swabbing. If you are really trying to get the nose lining cells, then you don't need to go 10 revolutions.

I always blow out my nose, but COVID is a "dry" disease for me. There just isn't much snot at all.

The directions state at least 5 times and 15 seconds. I know for a fact I'm not doing 5 rotations in 15 seconds, but much faster.

The directions are strict about the 6 drops. False negatives result from too much, so they say. Too few, well, not enough liquid to travel down the test strip.
Need to have a steady hand and firm finger strength for the BinaxNow. I could see some struggling, possibly elderly performing the steps on the Abbott test.

 

[dullard]

I always blow out my nose, but COVID is a "dry" disease for me. There just isn't much snot at all.

The directions state at least 5 times and 15 seconds. I know for a fact I'm not doing 5 rotations in 15 seconds, but much faster.

The directions are strict about the 6 drops. False negatives result from too much, so they say. Too few, well, not enough liquid to travel down the test strip.
Need to have a steady hand and firm finger strength for the BinaxNow. I could see some struggling, possibly elderly performing the steps on the Abbott test.

Yes, I know the manual states 6 drops and 3 swirls. I'm also stating that it isn't important to do exactly that many. It is just to guide the user to get roughly the correct amount.

Try slowing down. You are trying to collect cells, not race to see how many swirls you can complete in a second.

 

[WilliamM2]

When we caught it last year we had iHealth, QuickVue, and Abbott on hand. When first positive with iHealth, we then used QuickVue to confirm, Same results. Next day we tried the Abbot. Same results.

When we first tested negative we also used iHealth, and confirmed with Abbot. They all seemed accurate to me, but it's way too small of a sample size. Also all seemed easy to use, although the Quick view seemed like they would be easy to spill. Had to prop the little tubes into holders, and dip in test strips. Least user friendly.

Currently have Abbot and the last round of tests sent by USPS, which are Access Bio, Look to be just like the iHealth brand, but made in USA, not China. Haven't used them yet, but I also prefer that type.

 

[Geekbabe]

I have always gotten the Binax Now tests, they can be tricky to use but if you do the test in strong light & are careful you can get the 6 drops in the small top hole. Both times I had covid my positive results came up pretty quickly.