By Christopher Labos, MD, CM, MSc

Back when I was a resident, we always told patients to go do their blood test on an empty stomach. They would line up every morning at the hospital to get all their blood tests done, and every morning that line would stretch out the hospital doors and around the block. Then, by lunchtime, it was a ghost town.

You don't see that anymore for one simple reason. It doesn't really matter if you're on an empty stomach or not. We all know that for your [complete blood count], electrolytes, and most routine blood tests, it doesn't actually matter whether you've been eating or not. The only reason to do fasting blood tests is because of two things:diabetes and cholesterol.

Back in the day, fasting blood glucose was how we picked up diabetes. Now, most of us — I hope — tend to use hemoglobin A1c, given that it's a 3-month average of your blood glucose levels, and whether you ate breakfast or not isn't really going to throw it off by all that much.There's really no need to fast for most patients with diabetes.

The other issue is cholesterol. Ever since we started focusing more on LDL, we had a problem because LDL isn't directly measured in most labs. It's calculated using total cholesterol, HDL, and triglycerides.

Triglycerides can go nuts based on what you ate last night or that morning. To make sure everything was standardized, we told patients to be on an empty stomach when they did their blood tests. If the triglycerides were too high, you couldn't get an accurate calculation of the LDL.

Now, it turns out that nonfasting blood tests for cholesterol are not off by all that much.Sure, there are rare cases of patients with super high triglycerides for whatever reason, but for most people, the difference was minor.

Now, we have other tests like ApoB and we also check things like Lp(a), which are not affected by whether you're fasting or not. At this point, there's no real reason to do fasting blood tests.It maybe made sense 20 years ago, but not anymore.

It's also easier for people to get their blood tests at any time of day rather than everybody rushing in first thing in the morning. It just makes things a little bit easier for the patient getting routine labs — and that's progress.

Stop doing fasting blood tests. Your patients probably don't need them.