Are we talking about "hook effect?"

[RNfromMN]

I was skeptical after I heard about it over on the TB, just because I'd never heard it brought up with any of my other pregnancies. In case you haven't heard of it, it's the theory that a pregnancy test will actually get lighter the further along you get in your pregnancy due to (here's the part I don't fully understand) rising hcg levels.

I am skeptical no more! I took a test this morning (cuz I'm crazy like that) and got a little nervous that it was clearly lighter than one I had taken a couple weeks ago. I diluted the same urine with quite a bit of water (50%?) and that test came out even darker. The test on top is the one dipped in the diluted urine.

Just thought I'd share

[frecklesnbrains]

Oh, I love Wondfos. I'm guilty of having tested the hook effect on my own urine too a few weeks ago. I actually did 2 dilutions, and the most dilute sample gave the darkest line. I didn't take a picture though.

[jjh1119]

Wow, very interesting! I had never heard of it before.

[ArgyleEnigma]

Really? Why does that happen?

[teggy20]

I've never heard of that before but just reading about it makes me anxious (and I'm anxious enough ) I've been thinking about giving away the rest of my Wondfos so I'm never tempted to take another pregnancy test again!

[virginiaorjohn]

I've heard of this! How many weeks are you RNfromMN? Ever since we started with IVF, I stopped peeing on things. I bought a pregnancy test yesterday because I really just wanted to pee on something and have it be GLORIOUSLY POSITIVE for once, haha. Have t tried it yet! I wonder what it will do at 7.5 weeks...

[vivela]

I read somewhere that hCG levels actually peak around the end of the first trimester. A woman who is 40 weeks pregnant can have levels so low she tests negative.

[RNfromMN]

virginiaorjohn, I'll be 8 weeks on Saturday. Agree - there is something about that big fat undeniable +!

[frecklesnbrains]

So, because I'm a nerdy scientist-type, here's the explanation for the hook effect:

Pregnancy tests detect HCG using antibodies that specifically detect the hormone. The test strip is loaded with two different types of antibodies. One of these groups of antibodies is attached to the strip and basically immobilizes the HCG from the urine to that little spot on the strip that's going to change color. The second group of antibodies contains the color label, so once the little HCG molecules are immobilized on the strip the second set binds and causes the strip to change color.

The problem comes when your urine contains REALLY high concentrations of HCG. It basically over-saturates the whole system and binds up all of the second (colored) antibodies so that they can't then detect the HCG that's become immobilized on the strip. So you can get a faint line (or even a false negative). But, if you dilute your urine then the level of HCG is low enough that it doesn't over-saturate the receptors and the test works better.

[ArgyleEnigma]

Nov 12, 2015 14:51:04 GMT -5 frecklesnbrains said:

So, because I'm a nerdy scientist-type, here's the explanation for the hook effect:

Pregnancy tests detect HCG using antibodies that specifically detect the hormone. The test strip is loaded with two different types of antibodies. One of these groups of antibodies is attached to the strip and basically immobilizes the HCG from the urine to that little spot on the strip that's going to change color. The second group of antibodies contains the color label, so once the little HCG molecules are immobilized on the strip the second set binds and causes the strip to change color.

The problem comes when your urine contains REALLY high concentrations of HCG. It basically over-saturates the whole system and binds up all of the second (colored) antibodies so that they can't then detect the HCG that's become immobilized on the strip. So you can get a faint line (or even a false negative). But, if you dilute your urine then the level of HCG is low enough that it doesn't over-saturate the receptors and the test works better.

Cool! That explains why the control line is little lighter on the concentrated one too.

[frecklesnbrains]

Nov 12, 2015 15:00:40 GMT -5 ArgyleEnigma said:

Nov 12, 2015 14:51:04 GMT -5 frecklesnbrains said:

So, because I'm a nerdy scientist-type, here's the explanation for the hook effect:

Pregnancy tests detect HCG using antibodies that specifically detect the hormone. The test strip is loaded with two different types of antibodies. One of these groups of antibodies is attached to the strip and basically immobilizes the HCG from the urine to that little spot on the strip that's going to change color. The second group of antibodies contains the color label, so once the little HCG molecules are immobilized on the strip the second set binds and causes the strip to change color.

The problem comes when your urine contains REALLY high concentrations of HCG. It basically over-saturates the whole system and binds up all of the second (colored) antibodies so that they can't then detect the HCG that's become immobilized on the strip. So you can get a faint line (or even a false negative). But, if you dilute your urine then the level of HCG is low enough that it doesn't over-saturate the receptors and the test works better.

Cool! That explains why the control line is little lighter on the concentrated one too.

Yup!

[Andrea]

Nov 12, 2015 14:51:04 GMT -5 frecklesnbrains said:

So, because I'm a nerdy scientist-type, here's the explanation for the hook effect:

Pregnancy tests detect HCG using antibodies that specifically detect the hormone. The test strip is loaded with two different types of antibodies. One of these groups of antibodies is attached to the strip and basically immobilizes the HCG from the urine to that little spot on the strip that's going to change color. The second group of antibodies contains the color label, so once the little HCG molecules are immobilized on the strip the second set binds and causes the strip to change color.

The problem comes when your urine contains REALLY high concentrations of HCG. It basically over-saturates the whole system and binds up all of the second (colored) antibodies so that they can't then detect the HCG that's become immobilized on the strip. So you can get a faint line (or even a false negative). But, if you dilute your urine then the level of HCG is low enough that it doesn't over-saturate the receptors and the test works better.

Science ftw!!!

[babyzebra]

frecklesnbrains I love your science talk in this thread and randoms! Thanks for sharing all this!

[oceanhutt]

Nov 12, 2015 13:48:59 GMT -5 virginiaorjohn said:

I've heard of this! How many weeks are you RNfromMN? Ever since we started with IVF, I stopped peeing on things. I bought a pregnancy test yesterday because I really just wanted to pee on something and have it be GLORIOUSLY POSITIVE for once, haha. Have t tried it yet! I wonder what it will do at 7.5 weeks...

I wanted to do this but I don't want to spend the money but want that moment ya know?