The blue dye conspiracy
September 21, 2019 4:38 PM   Subscribe

Is the mistrust of blue dye pregnancy tests founded?

I've fallen into a few rabbit holes recently of looking at forums where people post photos of their pregnancy tests, including some photos where it's unclear whether the result is positive.

Overwhelmingly it seems that there is a mistrust of blue dye tests. If someone posts a photo of a faint positive on a Clearblue test, they are sometimes met with responses like, "I wouldn't trust it. I feel like that line is always there. Get yourself a FRER (First Response Early Result)."

On one thread someone wrote something to the effect of, "Everyone knows that blue dye spreads more. That's just basic science!" Um, what? Is that a known scientific fact?

So I did a bit more googling to try to find out whether any of these claims are founded. The only thing I really found was a doctor saying that blue dye tests can be less clear to people, and that evaporation lines are a grey colour. I guess that grey is not too far from blue, so maybe that's where the confusion comes in.

Is there any actual scientific basis to claims that blue dye tests are less accurate, or is it an old wives tale?

I'm sort of non-seriously considering whether it's a conspiracy by big pink dye.
posted by kinddieserzeit to Science & Nature (9 answers total) 1 user marked this as a favorite
Do I mean mistrust or distrust?
posted by kinddieserzeit at 4:46 PM on September 21, 2019

To answer your follow-up question, they basically mean the same thing and can be used interchangeably.
posted by Automocar at 6:07 PM on September 21, 2019 [2 favorites]

According to this study, the First Response tests detected 6.3 mlU hcg per ml urine, while the Clearblue tests detect 25. So a FRER might read positive while a Clearblue is still reading negative. But I don’t see any reason to mistrust a Clearblue positive.
posted by Kriesa at 6:13 PM on September 21, 2019 [1 favorite]

Re "old wives tale": as an old woman (though no longer anyone's wife), I respectfully ask that you not use this phrase to refer to nonsense of any type.
posted by she's not there at 9:49 PM on September 21, 2019 [20 favorites]

I mean, I went through IVF, along with all the IVF forums, and I never ever heard that this was a thing. I only ever heard "girl, if you're going to test 15 times a day, be sure you're buying your tests at the dollar store, or in bulk on Amazon:.

That being said, I remember that the digital tests were fantastic as they left no room for doubt, but they are pricey. But blue vs pink for results? Never heard of it.
posted by vignettist at 10:03 PM on September 21, 2019 [2 favorites]

Blue versus pink dye is certainly discussed on various forums in my experience.
posted by k8t at 4:47 AM on September 22, 2019 [4 favorites]

I've picked up A LOT of random info reading mumsnet and I've never heard this one. I have however read a lot that faint or not a line is positive so that the evap line thing is a myth. Notheing ever about blue dye being less trustworthy.
posted by kitten magic at 4:47 AM on September 22, 2019

I've had blues show up and not show up, if it shows up and subsequent tests are negative, it's likely that pregnancy did not progress.
posted by tilde at 6:04 AM on September 22, 2019

Here is a chart of the self-reported sensitivity of 60 test manufacturers (lower threshold = more sensitive):

Here is an article describing the history of home testing:

From the article:
"More than 60 brands of home pregnancy tests are available in the US market, although many of the brands are produced by the same manufacturers. Their analytical sensitivities range from 6.3 IU/L to 50 IU/L of urine, with most falling between 20 and 25 IU/L ( Even with these very analytically sensitive and specific tests, issues with false-negative results do occur when women test their urine too early, although advertisements for some tests state that a positive test result can be obtained several days before a missed menses. The reasons for a false-negative result include the observations that up to 10% of women may not even have implanted on the day of their expected menses, the amount of hCG secreted by the trophoblast during early pregnancy can vary by 10-fold, the monoclonal antibodies used in the test may not recognize the major forms of hCG present in the urine during early pregnancy, high concentrations of the β-core fragment of hCG can produce interference in some of the tests, and, rarely, the high-dose hook effect can occur (13, 19–21)."

All the sticks are ELISA tests testing for hCG molecules. Color doesn't matter, it's just how they tagged the capture antibody. The digital test just reads the color optically and displays as a number.

Kudos to you for looking beyond the marketing and anecdotal superstition to find the facts and science.
posted by dum spiro spero at 8:51 AM on September 22, 2019 [5 favorites]

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