Bitcoins are not currently legal in some countries so it is difficult to use in payment transactions. But I believe in the future bitcoin will be used for medical billing.
It is obvious that we should not use crypto currencies or Bitcoin in countries that it is illegal. Also, it is really hard to pay with Bitcoin if that platform don't really accept Bitcoin or any other crypto currencies, the worse they do not know it. But if I am not mistaken, there is this one crypto currency that focus on health, there might be others but that is what I can remember.