I wasn't really sure if your scheduling the biopsy appt and saying "we're doing it" meant your doctor said yes to it or you're going to be insistent. So, if that doesn't work how bout you "make him an offer he can't refuse" by bringing a red rider bb gun to your next appointment -JK!
OR
As Debi mentioned use SSDI as a reason.

I know you care about having a base to compare. I would too. I just don't know if your doctor does. This could be projection caused by my past few experiences with doctors.-

*Strike the last paragraph because I now know your doctor is on board! YAY!!