12yo son came home from school 1/31 due to nausea and sore throat. No fever at the time but did end up with a mild fever later in the day (99.8 on a kid that normally runs cool). Negative at-home BinaxNow antigen nasal swab test. Alternated tylenol/ibuprofen as per usual for sore throat after he was able to tolerate some liquids/foods.

He still felt pretty terrible in the morning (Tues 2/1) so we took him to the doc for a PCR test and to check for strep as the symptoms were pretty much like previous times he had strep.

Doc was fairly confident it was covid and was surprised when the PCR test came back negative. Strep also negative. The doc mentioned the possibility of a false negative and recommended to keep him home at least a few days but gave us a note clearing return to school. We kept him home Wednesday and school was closed due to weather Thurs/Fri. We 'might' have sent him Friday since he was pretty much feeling 100% by then but, due to weather, it didn't matter.

Identical symptoms (nausea, sore throat, mild fever) hit my wife last night and she just popped positive on an at home test.

So is it safe to assume my son had a false negative antigen test (not a big surprise) and a false negative PCR test (I thought that was rarer)?

Also, I'm sure this has been rehashed a billion times on here but, what is the difference, if any, between the 'rapid' PCR test done at the pediatrician's office vs. the PCR that has to be sent out to a lab?

Walgreens actually shows two non-antigen options:
Diagnostic Lab Test (PCR) with results in 2-3 days and Rapid Diagnostic Test (ID NOW) with results <24 hours

I'm wondering if the doc office test was actually more like the ID NOW test from Walgreens although they specifically referred to it as a PCR test.

I can tell you that when omicron rolled through my house, I had 1 day of mild symptoms but never tested positive at all. My husband and daughter only tested positive (rapid) when I swabbed their throats, not their noses. We are certain it was valid because my husband did have the loss of smell without congestion and antibodies shot up afterward. It does not seem to be that uncommon to hear about multiple negatives early in the disease course with omicron.

If the pediatrician's office didn't send out the sample, it's very possible he was positive. I've had multiple friends only test positive on the 24 hour+ PCR (especially if they are already vaccinated).

The rapid NAAT test is also referred to as a rapid PCR, because it amplifies and detects nucleic acids. But it's not as sensitive as the PCR that's done when you send samples off and they are amplified. PCR also amplifies genetic material but does so with much higher sensitivity. A lot of the sensitivity has to do with the exact procedure that is used (ie. how many amplification cycles are performed).

Both are more accurate than an antigen test. I personally would not retest with PCR to confirm a NAAT test result. I also would not continue testing if I had a negative NAAT or PCR test and my symptoms were resolving.

Thanks for the useful responses.

And I mostly agree that, assuming no new more severe variant pops up (i.e. something similar or worse than Delta as far as hospitalizations), we should be treating it like normal cold/flu.

I was 50/50 on whether it was covid or strep and wanted to be sure to be able to get antibiotics before the weather hit if it was strep. Negative on both was pretty confusing and we let our guard down thinking it was just a bad cold. He was mostly holed up in his room the whole time anyway but we could have been a little more careful when eating meals and such. 20/20 hindsight.

Yeah the rapid NAAT test we have has poor sensitivity per the manufacturer(Sofia). If it is negative we are supposed to send an official PCR to confirm the negative.

In my experience it has good sensitivity. I have yet to have a + PCR with a negative rapid NAAT.

This is so odd to me. Especially because there are entities using the NAAT test as an "official" result. That's how we got into Canada - with negative NAAT tests.

I don't really understand the point of developing more rapid tests if you're just going to send them off for PCR anyway.

What's interesting is, when you search online, most results indicate the two are pretty much equivalent. The lower sensitivity of NAAT is a minor point that sort of gets glossed over.

It's almost like sone groups only want to trust them for positives. If you get a negative you have to "confirm". That's not how testing should work.

I wonder if the issue is really with sample collection. Lots of places that do NAAT let you collect the sample yourself. Same variable applies to antigen tests.

This has been our corporate strategy for our global coworkers. Start testing in the morning of the 48-72 hour window. Keep testing until it's negative.

TXTransplant said:

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This is so odd to me. Especially because there are entities using the NAAT test as an "official" result. That's how we got into Canada - with negative NAAT tests.

I don't really understand the point of developing more rapid tests if you're just going to send them off for PCR anyway.

What's interesting is, when you search online, most results indicate the two are pretty much equivalent. The lower sensitivity of NAAT is a minor point that sort of gets glossed over.

It's almost like sone groups only want to trust them for positives. If you get a negative you have to "confirm". That's not how testing should work.

I wonder if the issue is really with sample collection. Lots of places that do NAAT let you collect the sample yourself. Same variable applies to antigen tests.

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It has been standard practice to confirm negative rapid strep with a culture for years. Only trusting positives on low sensitivity tests is very much standard of care and taught early in med school statistics. Rapid strep is 95% sensitive and we still don't trust it for true negatives.

Yeah, I knew cultures for strep were common, but I didn't realize the sensitivity was 95%. I thought it was much lower and false negatives were pretty common.

Also, there is antibiotic treatment for strep, so there is value in confirming a test result. Can't say the same for Covid, especially for cases with no or very mild symptoms.

TXTransplant said:

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Yeah, I knew cultures for strep were common, but I didn't realize the sensitivity was 95%. I thought it was much lower and false negatives were pretty common.

Also, there is antibiotic treatment for strep, so there is value in confirming a test result. Can't say the same for Covid, especially for cases with no or very mild symptoms.

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True for mild symptoms, but Paxlovid is pretty widely available now for 12+

Oh right…the Pfizer drug. Forgot about that. Is it being widely prescribed? Because I don't think I know anyone who has been diagnosed recently and taken it.

I honestly don't know. I've used it a few times on high risk patients.

Aston94 said:

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It's almost like we should just treat it like we do any cold or flu we have had in the past and not worry about testing unless it is a severe enough case to go to the hospital/doctor's office.

Testing/masking/counting all "cases" has to end now. There is no point anymore. Covid is now endemic and we need to all move on as a society. I watched the Olympics briefly last night and the mask virtue signaling/testing/limited crowds and "Olympic Bubble" made me switch off of them very quickly.

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You can throw in 'the having to have a negative test to fly home from outside the US' into that useless bucket as well