Scientific question about HCG test line

[Orangeflowers]

Hi all,

I have a question about test lines on early detection pregnancy tests. If I've used a test and the sensitivity is 10iu, should I expect that if the HCG in my urine is above 10iu then the test line will be as dark as the control? But if my test line is fainter than the control then that means that my HCG is lower than 10iu?

I'm just trying to understand if my test line is fainter than the control does that actually mean my HCG is less than 10iu or does the test start to detect HCG at 10iu with a faint line and the level has to be a lot higher than that for the test line to be as dark as the control?

I'm in the crazy tww, otd tomorrow and going mad! Understanding this better would help.

Thanks for any help.

[Purpledoggy]

You can’t compare intensity to the control line is this way as the control line detects something else. If your HCG is above 10iu a test line will be visible, the colour intensity proportional to concentration (unless it gets so high it starts to mess up detection aka prozone effect or Hook effect). The control line just tells you your test is functioning correctly. If you can see a test line, your HCG is above approx 10iu xx

[Orangeflowers in reply to Purpledoggy]

Thank you for explaining. I'm wondering if it is calibrated so that whatever is detected on the control line shows up in the same intensity as HCG should on the first day of a missed period, if that makes sense?My lines are still here at otd today and are as strong as yesterday but what worries me is that I'm using 6 days early tests and the test isn't as dark as the control yet. I would have thought that should happen earlier with earlier response tests?

I know I'm overthinking! I'll call the clinic tomorrow and see if I can get bloods xx

[Purpledoggy in reply to Orangeflowers]

Controls aren’t calibrated in this way, only to a level they should give a strong line to tell you the test worked. I forget what molecule is used as a control in PTs. 10iu hCG would be expected to give a less intense line than the control as it’s meant to be the limit of detection. Xx

[Fruitandflowers]

Don't think the control line measures HCG as it's there and dark when there's zero HCG, it just shows the test is working. It's always taken quite a while for my test lines to get as dark as the control and by that stage the HCG's been very high (into the 1,000s). Can only really compare control line with control line (and on the same brand and type of test) and even then it can vary a lot and won't tell you the level of HCG. The CBD with weeks indicators can give you an idea but can also cause a lot of stress, so if you can get HCG bloods done that's the only way to know definitively. Fingers' crossed for OTD!

[Orangeflowers in reply to Fruitandflowers]

Thank you 😊 I did a clear blue weeks indicator yesterday as I bought it before reading they were rubbish. It showed 1-2 weeks.

OTD was this morning. I still have lines which aren't lighter but aren't as strong as the control.

I'm hoping that I might be a bit behind as the frozen blastocyst hadn't fully re-expanded when it was transferred and was a lot smaller.

I'll phone clinic tomorrow and see if I can get bloods. I'm with care though and don't think they'll do, so might have to wait for Medichecks in the post xx