As a pharmacy student I asked my teacher about the Cockcroft-Gault equation in regards to transpeople. Since it isn't quite certain where the difference comes from, it isn't known which equation should be used for trans patients. The equation is only able to give an estimate based on averages and if you really need to know the renal function, doing the full work up that needs the urine collected over 24 hours is the only accurate method anyway. Since sex hormones change a lot and could alter renal function by themselves, I'd imagine a trans woman could be close to the male average at the beginning, but closer to the female average after a decade or so of taking hormones. But we just don't have scientific data to actually tell when which modifier should be used.

As for UTIs, that would also depend on whether the transgender person is operated or not. So pre-OP transmen could do with the "easier" treatment, post-OP they would probably fall into the complicated category. And that's not considering that it might be an OP-related infection if the OP wasn't too long ago.

It's definitely certain that medical professionals need to know the medical history to choose the best treatment. But whether the birth certificate contains the AGAB or the right gender, it may lead to the wrong treatment for trans people anyway. So using that as a reason to not be allowed to change it just seems like an excuse to me.