Do we need to fast before a cholesterol screening? Maybe not, suggests new study

By Deborah Kotz, Globe Staff

I haven’t had my cholesterol checked in close to two decades because I always forget to fast before my annual exam with my gynecologist -- who offers the routine blood test that adults are supposed to have at least every five years. I don’t want to bother going back for a separate appointment, which is an inconvenience that keeps a lot of Americans, besides myself, from getting regular cholesterol screenings.

But a study published Monday in the Archives of Internal Medicine suggests that most of us can skip the recommended eight-hour fast and still get reliable cholesterol measurements. The Canadian researchers examined medical records from nearly 210,000 adults who had their cholesterol levels tested in 2011 and found that total cholesterol levels and levels of high-density lipoprotein or HDL cholesterol, a marker of good heart health, remain fairly steady regardless of whether a person eats within an hour of the test or abstains from eating for up to 16 hours beforehand.

Neglecting to fast can, however, cause variations in the “bad” low-density lipoprotein levels -- often used to determine whether someone needs to take a cholesterol-lowering statin -- of up to 10 percent. Eating right before a cholesterol test can also cause triglyceride levels -- another type of blood fat -- to soar by as much as 20 percent above fasting levels.

But even with these caveats, “an awful lot of people probably don’t need to worry about fasting before getting cholesterol screening,” said Dr. J. Michael Gaziano, a preventive cardiologist at Brigham and Women’s Hospital who wrote an editorial that accompanied the study. “We’ve known about this already from previous smaller studies, and I’ve been thinking about eliminating the fasting requirement for some time.”

With this new result, Gaziano said he’s “moving toward doing more screenings and cholesterol monitoring” in patients who come to his clinic at the VA Boston Healthcare System and are due for a cholesterol check but haven’t fasted beforehand.

“I would much rather have a non-fasting sample than no sample,” he said, and very frequently he finds that patients, who haven’t fasted, don’t return to get a blood test later on. “Ideally, I’d like to get a cholesterol screen when they first come in and then have the results before they leave so we can discuss treatment options if levels are elevated.”

The National Heart Lung and Blood Institute’s current cholesterol screening recommendations -- which are expected to be updated early next year -- recommend that all adults age 20 and over have a fasting screening test every five years and that if the test is taken without fasting, doctors should consider the measurements for only total cholesterol and HDL to be reliable. The guidelines recommend a follow-up fasting screening if the HDL measurement is low -- under 40 milligrams per deciliter -- or if the total cholesterol is high, 200 mg/dL or above.

But Gaziano said a follow-up fasting test probably isn’t necessary to determine a course of action for poor cholesterol levels. Doctors can use the Framingham risk score calculation -- based on total cholesterol, HDL, smoking status, blood pressure, and age -- to calculate a person’s 10-year heart disease risk and determine whether cholesterol-lowering drugs or lifestyle modifications, such as increased exercise and a lower-fat diet, are warranted. “We don’t absolutely need an exact LDL measurement to make these decisions,” he said.

Where a fasting blood test might come in handy, however, is to reliably assess triglyceride levels in those who have insulin resistance, the precursor to diabetes, since high triglyceride levels often go hand in hand with the disease. Diabetics -- who often have to fast anyway before their doctor’s appointment to have their blood sugar levels checked -- should also aim to have a fasting cholesterol measurement to monitor their triglycerides.