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When to Test — And Why

By David Mendosa

Last Update: December 14, 2005

She controls her diabetes with medicine, diet, and exercise. Her most recent A1C result was 6.2. That’s not bad.

‘Test two hours after eating.’

Her blood glucose level goes higher after she eats than at any other time. That’s normal, but it’s not good. That's why Catherine Nord makes sure to check her level after each meal. More and more people are doing just that.

It wasn’t always so.

Very few of us even had blood glucose meters 25 years ago. And for most of the past quarter century when people with diabetes tested, it was usually before breakfast. But that’s changing.

Exercise and Testing
Another time to test is before and after heavy exercise, because all that exertion will bring down your level. If it’s low before exercise, you run a risk of going too low during or after your workout, particularly if you use insulin or one of the sulfonylurea drugs. A blood glucose level below 60 mg/dl (3.3 mmol/l) — known as hypoglycemia or familiarly as a hypo — is probably the least fun and most dangerous of any of the short-term consequences of diabetes.

Exercise has always been a great way to bring down your blood glucose level, as long as your level is not too high. But people with type 1 diabetes in particular should avoid exercise, if their levels are more than 250 mg/dl (13.9 mmol/l) and they have ketosis — high levels of acidic substances called ketones in their blood — or if their level is over 300 (16.7 mmol/l) even if they don’t have ketosis.

But until the beginning of this century besides exercising we had few if any other ways to prevent our blood glucose levels from spiking after any meal that includes carbohydrates. Since we couldn’t do much about high blood glucose after meals besides exercising, we had little reason to our check it.

We do now.

Controlling Levels After Meals
It’s only been during the past few years that we have been able to get diabetes medication that will prevent our blood glucose levels from going too high after meals. People who use insulin now have a choice of rapid acting insulin analogs. But most people who have diabetes use pills instead of insulin to control it. These people with type 2 diabetes can now take other medications just before their main meals that will help control their blood glucose level.

“We are going to have to get a whole new mindset to get people to test after meals,” William (Reddy) Biggs, an endocrinologist who has a practice in Amarillo, Texas, told me not long ago.

If using drugs like these means that people will start testing their blood glucose more often after their meals, it will be a good thing, Arturo Rolla, another endocrinologist told me not long ago. Dr. Rolla, who is on the staff of Beth Israel Deaconess Medical Center in Boston, says that for several years he has encouraged his patients to test after meals, rather than only their fasting levels.

Most of Dr. Rolla’s patients have their diabetes under good control. That means their A1C results is 7.0 percent or less, the target set by the American Diabetes Association (ADA) and most other organizations. The American Association of Clinical Endocrinologists (AACE) sets the target at 6.5 percent. People who don’t have diabetes have A1C levels of 6.0 percent or less. The A1C is the gold standard of diabetes management, measuring average blood glucose levels over the previous two or three months.

Who Needs to Test after Meals
We can now control blood glucose spikes after meals. But who will benefit most from testing then? How soon after eating is the best time to check our levels? And what target should we set?

Recent research based on studies of hundreds of people with type 2 diabetes show that high blood glucose levels after meals has a greater effect on A1C levels among people who, like most of Dr. Rolla’s patients, have their diabetes under good control than among those with poor control.

For example, when A1C results are low — less than 7.0 percent — mealtime glucose contributes about 70 percent of the A1C. However, when A1C results are high — greater than 10.2 percent — fasting blood glucose contributes 70 percent of the A1C value.

If your A1C levels are above 7.0 percent, you run a much greater risk of complications. That means getting your diabetes under control needs to be your top priority. But then you can concentrate on testing after meals.

When to Start Counting
But do we start counting from the beginning, the middle, or the end of the meal? And should we test one, two, or more hours after eating?

There is a great variation in the length of a meal. So it is more precise to start counting from the time of the first bite, Dr. Richard Hellman, the lead author of the AACE’s Diabetes Medical Guidelines Task Force, told me. Another reason to start counting from the first bite is because our glucose levels begin to rise about 10 minutes after the start of a meal, an ADA statement says.

Both organization recommend that most of us test two hours after eating. While your blood glucose level could be highest one hour after a meal, there are good reasons to wait until two hours after the first bite. Writing on a diabetes mailing list, someone called Helen said it best:

“If I aim for pre-meal levels to occur an hour after eating, I chance going low after two hours and for sure after three hours. My blood glucose level tends to decline from hour two to hour three. Therefore I do not test one hour after — there is nothing I would do with that information other than aggravate myself.”

The exception, according to the ADA, is women who have diabetes and are pregnant. They could benefit more from testing one hour after eating.

The point of testing is to help you bring your levels down. So your minimum goal might be just reducing your level over a period of days or weeks.

The After-Meal Target
Several different organizations have set targets for blood glucose levels two hours after a meal. The ADA has the easiest target, less than 180 mg/dl (10 mmol/l). The International Diabetes Federation and the World Health Organization recommend a target of less than 160 mg/dl (8.9 mmol/l). The American Association of Diabetes Educators, the AACE, and the American College of Endocrinology have the most aggressive targets, under 140 mg/dl (7.8 mmol/l).

Whatever target you accept, you might bear in mind that people who don’t have diabetes seldom have a level of more than 130 mg/dl two hours after a meal. If you check your level after each meal like Catherine Nord does, you will be able to have a lower blood glucose level, a lower A1C result, and less chance of complications. 


    David Mendosa is a freelance journalist and consultant specializing in diabetes and lives in Boulder, Colorado. When he was diagnosed with type 2 diabetes in February 1994, he began to write entirely about that condition. His articles and columns have appeared in many of the major diabetes magazines and websites. His own website, David Mendosa’s Diabetes Directory, established in 1995, was one of the first and is now one of the largest with that focus. Every month he also publishes an online newsletter called “Diabetes Update.” He is a co-author of What Makes My Blood Glucose Go Up...And Down? (New York: Marlowe & Co., August 2003).


This article originally appeared in Type 2 Life, Fall 2005.


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