A patient once asked me why I was ordering just a few diagnostics for him and not a “whole battery” of tests.

“Why don’t you just order everything? What do you think is going on?”
I realized that the patient was not asking for a differential diagnosis, but rather inquiring as to how I was going to solve the mystery of his illness. I improvised a story on the spot:

“Imagine you went to turn on your television set and it didn’t work. You would make a list in your mind of possible causes: Is the TV plugged in? Does the remote control need new batteries? Did a circuit breaker trip? And then you’d check each of those things out step by step. You’d look behind the TV to check the plug. You’d change the batteries in the remote. You’d run down to the basement to check the circuit breakers. And you’d examine each possible cause until you found and corrected the one problem keeping you from watching TV.

“Well, I’m doing the exact same thing with you. I have a list in my mind of maybe ten things that could be causing your symptoms, and I’m ordering tests to eliminate them one by one. There’s no point ordering an expensive test to determine if, say, number eight is the problem, when simpler tests might determine that it’s number two or five. Just like you wouldn’t immediately bring the set in for service until you’d checked the simpler possibilities.”

He got it.