22dp5/6dt - High Dose Hook Effect

Since my friend was kind enough to send me an entire box of pregnancy tests, I've been taking one every morning with FMU. I like seeing the two dark lines pop up as a sort of reassurance that everything is still okay in there since we haven't had an ultrasound yet.

The lines have always been nice, dark and reassuring until this morning. I actually slept in a bit later today and tested with a solid 8 hour hold. To my horror, the test line was lighter than the control line, lighter than the test the day before, OMGWTFAHHWHATWASGOINGON? I told myself the test was crappy, and it was, even the test line was lighter than normal, and resolved to test again after a 4 hour hold. Oh my god, holding your bladder and pregnancy do not go well together. I made it exactly 4 hours, rushed to the bathroom, and although the test was a little darker, it wasn't as dark as it should be. That's when it hit me right in the face, the high dose hook effect. Duh. I've experience it myself with ELISAs in the lab but I didn't think to apply it to a pregnancy test. Duh duh duh.

The high-dose hook effect is a well-known phenomenon in laboratory medicine, Dr. Gronowski says. It occurs when increasing concentrations of analyte lead to saturation of both the capture antibody and detection antibody, preventing formation of a complete antibody-antigen-antibody sandwich and leading to possibly false-negative results. She co-authored a study focusing on what she calls a “variant hook effect” that affects qualitative urine hCG tests. “The problem is an excess of one form of hCG. Part of the problem is that hCG comes in many different isoforms, and after five weeks of pregnancy, you get much more of one variant form called the β core fragment than you get of the hCG intact molecule. We demonstrated that if you add increasing concentrations of β core fragment to a urine sample that contains intact hCG, there is a dose-dependent inhibition of signal. This is similar to the standard hook effect, except that in many cases the devices don’t recognize β core fragment alone. In other words, the β core fragment only binds one of the two antibodies used in the assay, but it still has the same net effect and causes a false-negative result.”  (Check out the full article here)

And now it makes sense. At a day short of 6 weeks, I bet my β core fragment levels are much higher than my intact HCG. Obviously, I had to test this out by peeing on more sticks. 

And look at that! The solution diluted 50/50 with water has the darkest test line by far. Clearly, it looks like my stick peeing days have come to an end. There's no way I'm diluting cups of pee at 5 in the morning to get a satisfactorily dark line. I think I'm going to have to rely on blood tests and ultrasounds to reassure me from now on, as tough as that's going to be. The next blood test is tomorrow morning but my ultrasound won't be until Friday and after that, who knows. I hope my OB/GYN is open to frequent appointments to soothe my nerves :/