Fasting for blood test can lead to hypoglycemia in patients who take diabetes medications

Fasting before getting your blood drawn for cholesterol tests is common practice, but new research from Michigan State University shows it is a contributing factor of low blood sugar, or hypoglycemia, in patients who take diabetes medications.

The study, published in the International Journal of Endocrinology, shows that people with diabetes are more likely to experience FEEHD - fasting-evoked en route hypoglycemia in diabetes - than they would if they hadn't fasted. The "en route" comes from patients who have an episode while driving to a lab for blood work.

Saleh Aldasouqi, an endocrinologist in the College of Human Medicine, explained that eating before a lab test does not alter the results of the pivotal components of the cholesterol test as previously thought. In fact, fasting for these tests can incite hypoglycemia in patients 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," Aldasouqi said. "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. Our new motto is 'Feed not FEEHD', to remind patients of this danger and get them to eat."

Hypoglycemia happens when blood sugar levels drop below 70 mg/dl and can cause faintness, confusion and even a loss of consciousness. Severe hypoglycemia can cause acute harm to the patient or others, especially if it causes falls or motor vehicle accidents.

Aldasouqi said that routine fasting is based off guidelines from the 1970s and newer studies show it may not be necessary anymore. Canada and Europe have already changed their guidelines and no longer require fasting for lipid tests, the most commonly ordered fasting labs. Similar U.S. guidelines have not yet become mainstream. In view of the risk of FEEHD, Aldasouqi hopes for diabetes organizations to take a lead in disseminating these emerging changes on lipid testing.

The study showed proper education about fasting and diabetes also is lacking. Only 35 percent of patients surveyed indicated having received any FEEHD prevention instructions from their doctor prior to their lab visit.

"We encourage patients who receive orders for a lab test to ask their doctor if fasting is really necessary, and if so, how they should handle their diabetes medications during the fasting period to account for the changes in their blood sugar levels," Aldasouqi said. "FEEHD is overlooked in clinical practice, and we aim to bring this problem to light and further educate doctors and patients about the consequences of fasting while on diabetes medications."

The study involved 525 patients with diabetes and was conducted at two endocrinology practices in Michigan. Patients completed a two-page survey and were excluded if data was missing or they reported no fasting labs in the previous 12 months. Aldasouqi plans to conduct a larger, population-based study to determine the prevalence of FEEHD in the general population.