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 the normal ejection fraction (EF).

Systolic heart failure with only 25% of the blood volume pumped out is definitely a significant problem, and associated with a risk of deadly rhythm disturbances like ventricular tachycardia. This is why patients in that category often get an implantable defibrillator. But many people with ejection fractions in the 25% range look and act almost like anybody else during ordinary day-to-day activities.

Another set of numbers that can cause panic and confusion is the stages of chronic kidney disease. Specifically stage 3. I tell people that the founders of the nephrology speciality were either idiots or just plain cruel because they defined stage 1 and 2 chronic kidney disease as changes that routine testing can’t detect. So the first sign of trouble is automatically called stage 3. This is possibly designed to make primary care physicians look stupid. We follow patients for years and suddenly they have stage 3 of this feared (and often overrated) problem – we must obviously have been negligent and asleep at the wheel to have missed some early warning signs.

Stage 1 hypertension is a less dramatic numeric disease label that I see stamped on patients unnecessarily, especially by emergency room doctors. Elevated blood pressure when a person is in acute pain or fear is physiologic – an adrenalin mediated fight or flight response we share with all other animals, maybe with the exception of opossums.