Confusing numbers in medicine

Numbers ought to be obvious and straightforward in all walks of life, one would think. But there are many sets of numbers in medicine that confuse people.

The other day a patient told me tearfully that her brother’s heart was only working at 25%. I told her I was pretty sure that he had only lost half of his pump function and not 75%.

I explained that a beating heart never contracts so completely that there is no blood left inside it. Instead, only about 55% of the blood inside it is pushed out with every beat. That 55% is what we call