Do diabetics really need to fast for blood tests?

Diabetics don't have to fast before a blood test.
Diabetics don't have to fast before a blood test.

Fasting before a cholesterol blood test is just a nuisance for most people, but for those with diabetes, it can be dangerous.

New research shows that up to 22% of people with diabetes who fasted for lab tests had a low blood sugar episode (hypoglycaemia) while waiting for the test. The researchers also found that only about one-third of those who had a low blood sugar episode had received any education about how to avoid it when they were told to fast for lab tests.

Blood sugar level at zero

What's more, fasting for lab tests is likely unnecessary, too, the researchers said.

"The commonest test for which millions of people fast is cholesterol. But for the most part, fasting isn't necessary. Most doctors don't know. But in Europe and Canada the guidelines already say you don't need to fast," explained the study's lead author, Dr Saleh Aldasouqi. He is chief of endocrinology at Michigan State University.

Low blood sugar can be very dangerous for people with diabetes if they're not educated about how to look for it and treat it. The researchers said they found a case report from Thailand detailing a tragic incidence of low blood sugar in a woman who had fasted for her lab tests. Her heart stopped in the waiting room and she couldn't be revived.

Tests showed her blood sugar level was at zero. Normal fasting levels are between 70 and 100 milligrams per deciliter (mg/dL) of blood. Anything below 70mg/dL is considered low, according to the American Diabetes Association.

When he was practicing in rural Mississippi, Dr Aldasouqi said patients regularly had to drive an hour or more to get to his clinic. A low blood sugar episode en route could end in a traffic accident.

The new study included more than 350 people from two endocrinology practices in Michigan. Patients completed a two-page survey about their experiences. Their average age was 61.

No need to skip breakfast

Seventeen percent experienced low blood sugar provoked by fasting for a lab test, the findings showed. Of those who were high-risk for low blood sugar because of their medications, 22% had hypoglycaemia while waiting to have their lab test done.

Dr Aldasouqi isn't saying that cholesterol control isn't important for people with diabetes. In fact, he said that most, if not all, people with diabetes should already be taking cholesterol medication.

What he is saying is that people with diabetes don't need to skip breakfast to get an accurate cholesterol test done. He said doctors in the United States have been slow to adopt the guidelines already in use in other countries.

Dr Joel Zonszein is director of the clinical diabetes centre at Montefiore Medical Center in New York City. He said some people must fast for a particular procedure or have doctors who won't budge on fasting for lab tests.

Among patients, those most at risk of having low blood sugar while fasting are people on insulin or medications in the sulfonylurea or meglitinide classes. Because they must take insulin, people with type 1 diabetes are more likely to get into trouble fasting.

More effective medications

Dr Aldasouqi added that the elderly and people who have developed so-called hypoglycaemia unawareness also have a high risk of dangerous low blood sugar.

Dr Zonszein said this study also shows a need for education about newer options for treating type 2 diabetes. Patients don't necessarily need to take medications that can lower their blood sugar too much.

"There are more effective medications, with greater benefits," he said.

People who must fast need to talk with their doctor about how to manage their medications while fasting, Dr Zonszein said.

Results of the study were published recently in the International Journal of Endocrinology.

Image credit: iStock

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