Experts say there are things you can do before these tests, including adjusting medication and eating a small breakfast.
Skipping breakfast — or even delaying it a few hours — for the sake of a “fasted blood draw” isn’t a big deal for most people.
For people with diabetes, however, suddenly skipping breakfast can lead to dangerous fluctuations in their blood sugar levels if they aren’t taught how to properly adjust their medication regimen.
While countries such as Canada and Europe no longer require fasting for cholesterol tests, the United States still follows this outdated guideline, according to Dr. Saleh Aldasouqi, an endocrinologist in the College of Human Medicine at Michigan State University and lead author of the study recently published in the International Journal of Endocrinology
Fasting is considered a critical part of obtaining accurate test results in the many healthcare systems when measuring for certain cholesterol, liver, kidney, and glucose levels.
Aldasouqi told Healthline this approach is based on standards established in the 1970s, and it’s unnecessary, especially for people with diabetes.
“Hypoglycemia is an overlooked problem that we see from time to time in patients with diabetes who show up for lab tests after skipping breakfast,” explained Aldasouqi.
“Patients continue taking their diabetes medication but don’t eat anything, resulting in low blood sugar levels that cause them to have a hypoglycemic event while driving to or from the lab, putting themselves and others at risk,” he said.
The issue has become common enough to earn its own acronym: FEEHD, which stands for “fasting-evoked en route hypoglycemia in diabetes.”
Hypoglycemia, more commonly referred to as “low blood sugar,” usually begins with symptoms of lightheadedness, shaking, sweating, and feeling weak.
It can eventually result in losing consciousness, seizure, and death if not treated in time.
Many diabetes medications used in treating type 2 diabetes lower blood sugar levels by a combination of increasing the body’s insulin secretion and increasing its overall sensitivity to insulin — both of which could result in low blood sugar if the patient skips a meal.
These medication dosages are prescribed based on the expectation the patient is consuming their usual calorie and carbohydrate intake.
By suddenly asking a patient with diabetes to skip breakfast without instructing them how to safely adjust their medications can be dangerous.
Hypoglycemia while driving to the hospital for fasted blood work can be fatal for both the driver and others on the road.
For patients taking sulfonylureas — a category of diabetes medication under brand names such as Glipizide or Glyburide that increase insulin secretion — a doctor should instruct patients to skip these doses in the morning if they’re fasting for blood work, said Mara Schwartz, RN, CDE, and diabetes program coordinator at Self Regional Healthcare in Greenwood, South Carolina.
For people with type 1 and type 2 diabetes taking insulin, Schwartz said low blood sugars from skipping breakfast are easily avoidable.
“If a patient’s background or long-acting insulin doses are properly fine-tuned for their body’s needs, they shouldn’t have lows just from missing breakfast,” Schwartz told Healthline. “You should be able to not eat all day long and your blood sugar should be fine because that’s what your background insulin is intended to do: manage your baseline blood sugar levels.”
“If you’re not eating breakfast, then no, you shouldn’t be taking your fast-acting insulin that morning because that insulin dose is meant to cover the carbohydrates, fat, and protein in your meal,” added Schwartz.
“If your blood sugar is high when you wake up, you should still be able to take your usual correction dose of insulin to bring your blood sugar down to a safe level, but remember that it takes insulin up to four hours to bring your number down to a safe level,” she said.
While fasting — including regular intermittent fasting — can be practiced safely by people with type 1 and type 2 diabetes, it requires a certain degree of knowledge and preparation.
The recent study reported that only 35 percent of patients received any education regarding safely managing their blood sugar for fasted blood work.
Schwartz agrees that in her work, they see this issue constantly.
“Everyone’s health literacy level is different,” said Schwartz, who’s lived with type 1 diabetes for more than 30 years. “Some patients know how to adjust their own insulin doses for situations like this, but many don’t.”
Schwartz added that too often she sees patients with blood sugars as low as 40 mg/dL when they arrive for blood work after fasting.
Patients can end up in the emergency room because they weren’t taught to contact their doctor if they get seriously ill in order to safely adjust their diabetes medications.
Schwartz emphasizes a common concern among diabetes specialists these days: There needs to be better instruction, education, and communication between doctors and patients.
While more referrals to certified diabetes educators would help, Schwartz says they would still need an order from the prescribing doctor to make changes in insulin doses.
Regardless, eating food prior your blood draw is also an option, but what you choose to eat matters.
“If you are going to avoid fasting, it still matters what you choose for breakfast because a meal high in saturated fat can throw off some of your results,” said Schwartz. “Talk to your doctor about having a serving of fruit or something similarly healthy to prevent low blood sugars before having blood drawn.”
On the other hand, high blood sugar levels can also occur in patients with type 1 diabetes who skip breakfast because of the normal physiological reaction from the liver to release glycogen and convert it to glucose for the body to use as fuel.
While this process can occur in people without diabetes, too, a healthy pancreas compensates for this by releasing a small bolus of insulin. In a person with type 1 diabetes, this response is hard to predict and hard to dose for unless they’ve had time to experiment safely through trial and error.
But for many, fasting for the sake of blood tests should simply be avoided, because making the necessary adjustments in a patient’s usual medication regimen could complicate their diabetes management later in the day.
The safest bet for avoiding low blood sugars on the morning before a blood draw? Talk to your doctor about the idea of eating a small and healthy breakfast before heading out the door.