This could be a little bit of a unique situation, but it seems that there is no way of knowing what your health and shield combined total is when it goes above 75 total. Are we not supposed to get up that high or was it not thought of?
I had the bounty board which helped me store level ups, the item that gives a shield upon level up, and two copies of the spell that doubles shields. With the two fountains on level 5 I was able to cast the spell 6 times and gotten my combined health and shields up so high that I was able to kill the two balrogs and still have 75+ left over.