Faint control line on BinaxNow Covid test

September 7, 2022 7:17 AM

I've taken 4+ BinaxNow Covid tests over the last few days due to contact with someone who is testing positive. Each time, the test's control lines have been present, but more faint or splotchy than I would expect. I believe I am following the test directions correctly, but is this an indication that either I'm doing something wrong or the tests are bad? Can I trust the negative results?

An image of one of the tests, demonstrating the negative test with a weird control line

None of the tests have had any hint of a positive sample line.

In accordance with the directions, I am adding 6 drops of the test fluid to the top hole, avoiding touching the tip to the card, opening the swab on the "stick" end, swabbing for at least 15 seconds (usually more) on each nostril, going at least 3/4ths of an inch deep into each nostril (trying to slowly swab all sides, usually going deeper), inserting the swab in the card so that the tip is visible in the top hole, closing the card, and reading the test after 15 minutes.

Is this some kind of manufacturing defect? An issue with how I am administering the test? Should I be adding more or fewer drops? Swabbing differently? Or is this totally expected and normal for this type of test?

Can I trust these results?

posted by arcolz to Health & Fitness (8 answers total)

I think that's just what the Binax tests look like - the line is not as clear and dark as on the little plastic cartridge tests like FlowFlex. I have a lot of photos of negative tests on my phone (often need to share them for music rehearsals/performances) and the Binax tests all look like that.
posted by mskyle at 7:25 AM on September 7, 2022 [3 favorites]

My daughter tested positive in the ER. She has been using the same test you have at home. The first was negative, with a similar control line to yours. Then she got two positives with a more defined control line. Then she got a bad one with a blue control line. Then got another positive. This is over the course of a week to see if she can go back to school. The lines have varied in their definition. But I don't know why the first was negative and she definitely had a bad one as well.
posted by maxg94 at 7:28 AM on September 7, 2022

That line looks typical to me. BTW, are you also rotating the swab 3 times before closing the card?

At this point we are also testing up to 5 or 6 days after exposure.
posted by happy_cat at 7:42 AM on September 7, 2022 [1 favorite]

That looks within the range of my Binax tests. Btw, the only thing afaik that will control (heh) the control line exposing is if any/enough of the fluid soaks the test strip where the control line--how you swab doesn't matter (although as happy_cat said, spinning might matter some, but you should make sure you spin to try to make sure enough potential virus gets in the solution for the test line). Six drops in the hole, keeping flat and then closing properly is probably the bulk of it. It just tells you "yes, the test line would have been soaked as well". Which it is AFAIK. You can trust it insomuch it didn't detect enough virus to show the test line (which doesn't mean definitely negative, sadly).
posted by skynxnex at 7:55 AM on September 7, 2022 [1 favorite]

In my experience, the BinaxNow control line can show much more of a gradient than the various other RATs I've used, probably related to the slightly different means of exposing the sample to the testing solution.
posted by praemunire at 7:59 AM on September 7, 2022

Response by poster:

BTW, are you also rotating the swab 3 times before closing the card?

Yes! I forgot to include that step in the text of the question, but I have been doing that when administering the test. I've also been careful about keeping the test card flat while doing the other steps and during the waiting period.
posted by arcolz at 8:07 AM on September 7, 2022 [1 favorite]

inserting the swab in the card so that the tip is visible in the top hole, closing the card,
This looks typical to me for the BinaxNow test. But are you rotating the swab three times after inserting the swab but before closing the card? That's what my BinaxNow instructions say to do.
posted by twelve cent archie at 8:08 AM on September 7, 2022

I think I have taken every COVID test available to humankind multiple times at this point, and in my experience so far the BinaxNow tests tend to have fainter, less consistent control lines in general (I have never seen a positive test line in person).

One thing you didn't mention, though: Did you check the expiration date? The FDA has approved extensions from the date listed on the package for many tests, but I've definitely dug out a couple of the very first BinaxNow tests I got and stashed away and found that they're officially expired even including the extension. I don't know how that's supposed to affect the test result but I'd want to confirm that the test isn't also expired on top of just having a normally faintish line.
posted by rhiannonstone at 9:11 PM on September 7, 2022