Technical Q: HPT sensitivity vs beta sensitivity

epphd

OK, let's see if I get this right.

HPTs measure the hCG in your urine and average 25-50mIU/ml sensitivity. So that means they will register a positive when there is 25-50mIU of hCG per mililiter of urine. 

Beta hCG tests measure the hCG in your blood, and guauge that in terms of mIU/ml.  So, a positive beta of 50 would mean 50mIU per mililiter of blood.

So one measures blood and one urine, obviously enough, and they happen to use the same unit of measure.  But why would we ever expect there to be a quantitative correlation between the concentration of hCG in our blood versus urine?  I mean, so many things effect urine concentration of solutes - your kidney and liver function, hydration status, salt balance, etc.  Certainly qualitatively a high urine concentration probably means a high blood concentration, but that should be about it, right?

Or... maybe you guys already figured this out and I'm the only doofus who looks at a positive FRER and thinks "it's sensitivity is 25 therefore my beta today would be 25". 

Dear god Friday can't get here soon enough!

jodynjames2005

First of all, congrats!!

Secondly, it's just not that simple with HPTs. A lot of them will register far less than 25 hcg and sometimes they are randomly super faint for no reason. I got my first BFP (with triplets) at 6dp3dt (9dpo) and it was REAAAAAALLY faint and you could barely see it. I did not get a BFP with a digital until 8dp3dt (11dpo). At 13dpo when I had my beta, it was 265. If you go backwards, my hcg should have been about 132 at 11dpo when I got the BFP on the digital, so why the heck did I get a BFN on it the day before?! And why were my pee sticks do damn faint the entire time to begin with?!

To put it mildly, pee sticks are pretty unreliable in terms of using them to figure out your hcg. It's pretty much yes or no, nothing more and nothing less.

LVBlvd

Interesting...I thought the same way, but your point makes me realize that this is totally off!! ?Another thing to remember, even two tests in the same box can have different sensitivities.

?One thing for sure...if you got a BFP on a FRER, your beta would AT LEAST be 25. ?Therefore (if you got your BFP today), you could expect your beta to be around 75 (or more). ?

One more thing is for sure...you are PREGNANT!!! : )?

epphd

JodyNJames - that's exactly my line of thinking - particularly moving backward.  If I "want" (hah!) a beta of 150 on Friday, then by tomorrow it should be 75 and I should register a positive on virtually anything. 

I am insane.  I need to back away from the pee sticks. 

Thank you both!

jodynjames2005

I POAS twice a day, every day, from the day of ET... so, clearly, I too needed to back away! I'd still pee on them until I ran out even long after my THIRD beta, as if just getting a BFP even meant anything at that point. So, don't worry, you're not the only pee-stick-aholic!

P.S. Can you add me to your blog? I used to read it and just realized that it went private. My email is jodyajohnson@gmail.com.

LucyPevensie

jodynjames2005:

First of all, congrats!!

Secondly, it's just not that simple with HPTs. A lot of them will register far less than 25 hcg and sometimes they are randomly super faint for no reason. I got my first BFP (with triplets) at 6dp3dt (9dpo) and it was REAAAAAALLY faint and you could barely see it. I did not get a BFP with a digital until 8dp3dt (11dpo). At 13dpo when I had my beta, it was 265. If you go backwards, my hcg should have been about 132 at 11dpo when I got the BFP on the digital, so why the heck did I get a BFN on it the day before?! And why were my pee sticks do damn faint the entire time to begin with?!

To put it mildly, pee sticks are pretty unreliable in terms of using them to figure out your hcg. It's pretty much yes or no, nothing more and nothing less.

Yep, yep, and yep.  You can't go by the sensitivity ratings either - a test that claims it can detect an HCG of say, 25, may actually be able to detect an HCG as low as 12 - but 25 is what they've come up with based on studies they've done where their tests were most accurate beginning with an HCG of 25.  So you can't take one of those and say, oh, my HCG is at least 25 - not necessarily - it may be slightly lower.  Or not.  And some have more dye than others (same brand) - and sometimes like you said your pee is different so the concentration of HCG even in your own urine will vary..

Basically - it's easy to make yourself koo koo.  I think you'll get a positive on a digital tomorrow morning, FWIW.  And I know you're trying to hold out until Thursday 'til you pee on another digital - but I say, why wait!  It's only money! 

dusk42

You do need to back away from the pee sticks. ?:) ?But it is so hard! ?

I also read (while researching trigger shot clearance for someone) that only about 1/10th of the serum concentration of HCG is detected in your urine as you are clearing the shot. ?Obviously it is not the same situation, but that at least gives you an idea of the differences you are dealing with. ?

And FWIW, I had a beta of 115ish 12dpo, so I should have had something around 50 at 10 dpo (when I got a + digital) and around 25 at 8 dpo (when I got a negative on a line test). ?It does bother my science side that it's not nice and exact and linear and n=3+. ?

Also, they say that beta numbers can vary between labs as well. ?Just to add another level of complexity. ? ??

But I'm so glad to see you over here!?

Tryingtogetpregnant

Can you beg to get your beta moved up? They make you wait way too long!

 

DavezWife

I'll throw my deal into the pot, since it's weird... sunday was about 12dpo, and I got a + on a HPT. Got my beta drawn 34 hours later, and it was 25.  So either the htp picked up something low (say 12) or my numbers are going down. (I'm thinking the 1st, since lines are still strong today, and I am not bleeding or cramping, and I wish to remain hopeful)

 

na24

First, congratulations! ?This post makes me so happy.

?

Second, don't rely on what the HPT boxes say (or what the internet tells you) about what will and will not register on HPTs. ?Especially FRER. ?In 2007, I had a beta of 12 and then took a FRER the next day and got a decent line, so I thought it must have doubled and I went around telling my parents, et al. that things were looking good. ?The lines never got darker, and my next beta was 14. ?I was stunned because I thought relying on the claim of 25+ made sense. ?It didn't. ?And this also means that FRER can pick up betas as low as 14.

And then two months after that, I got a very faint line on a FRER and my beta was 4. ?Seriously. ?You'd think that the FRER people would want to claim that they picked up even the lowest numbers, but I guess something prevents them from doing that.

That said, I am fully confident that your beta will be a big, beautiful number. ??

RobynK

Yep -- what Jody said

FWIW -- my RE wanted at least 50 for a beta at 14dpo.  I think you'll be 15"dpo" (not sure what you call it on a DE cycle?) on Friday, right?  PLEASE don't panic if it's not at 150 like you want.  I think you should be more realistic and shoot for something over 50, or at least keep it in the back of your mind that over 50 is great at that point.

I'm so excited for you and can't wait to see your beta numbers!  We LOVE having you post on this board

skoorbnibor

here is another perspective... I got a beta done (I didnt know, My RE routinely does a beta when you come in 5dpt for progesterone blood work) on 5dp5dt  and later found out the result was 65. I took a FRER that night, and it was negative. I took another the next morning and it was positive. I took a digital and it was negative, took a cheapie, positive. That digital SHOULD have been positive, since the day before my beta was 65! I took another digitial 8dp5dt and finally it was positive. FWIW, my beta 2 days later was 680...

So even though we assume the digitial will pick up anything over 50, it isn't always true. The last time you peed, how much fluid you took in, what you ate, all sort of reasons why your urine might be diluted, and a test might not be positive. 

JGirl2005

I got a positive on a OPK before and I think those are not that sensitive.  So I wonder what all of it means too...I'm analytical like you.

 

Germanwife2b

There are too manay smart people on this board!!!

 

Congratulations and if you can, sit back and relish in the beauty of a positive pregnancy test!  I am beyond happy for you and wish there was some way I could speed warp you to Friday to ease your very smart, scientific and currently overworked brain!  I can't wait to see your daily updates!!!!!

hopeful14

I will share my own experiences with you, good and bad and hope you don't mind.... With my chemicals, I would always have a line on FRER, although the line was faint, there was no squinting required... my betas were 40 the first time and 19 the second time. With my current pregnancy, the test line was way darker than the control line and showed up right away... no wonder, my beta was 890!!! We are all rooting for you and cannot wait for Friday!!!!! Good luck!!!!!