Blood Sugar Monitoring: When to Check and Why

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Blood Sugar Monitoring: When to Check and Why

Checking after meals

Dr. Ganda agrees that premeal monitoring is a critical tool in diabetes management but says that sometimes postmeal readings are needed.

For example, postmeal readings are beneficial when a person’s fasting and premeal readings are in range, but his HbA1c level is high. Postmeal, or postprandial, readings are also important to assess a person’s response to short-acting pills that are taken just before meals or to the dose and timing of rapid-acting insulin given before meals. It can also give a sense of how much a person’s blood sugar level rises in response to certain foods or amounts of food.

“Diabetes is such an individualized disease that responses to foods vary from person to person,” Dr. Ganda says. “Unless people monitor after a meal, they will not understand the relationship between food and blood sugar. However, postmeal readings aren’t very useful unless you have premeal readings to compare them to.”

The most important time of life to check after meals is during pregnancy. “This is the only time we know for certain that postmeal readings have a direct and proven effect on outcomes,” Dr. Basu says. “For both mother and child, it is critical that pregnant women with diabetes monitor their blood sugar after meals.” Blood sugar goals for women with diabetes who are pregnant are “tighter” than those for adults who are not pregnant.

For people who choose to monitor after meals, the clock for when to check starts counting down at the start of the meal. Some people with diabetes monitor one hour after the start of meals in an effort to find their peak blood sugar level, then work to prevent spikes above certain levels. However, the experts say that’s not a good idea and that there isn’t any clinical, peer-reviewed data to support monitoring at one hour. The after-meal blood sugar goals for nonpregnant adults published by major diabetes organizations currently specify levels two hours after the start of meals.


“Looking at normal physiology, blood sugar peaks after you eat,” Dr. Ganda says. “For a person who doesn’t have diabetes, the peak occurs at 45 minutes to an hour after the meal. With diabetes, you peak a little later, and two hours is the standardized amount of time for blood sugar to come back down. There’s no need to check at one hour, because it is hard to interpret the numbers. It may be the peak at one hour, or the peak may not have occurred yet. Every person is different.”

Exactly what your blood sugar level should be two hours after meals is up for debate. As of 2017, ACE guidelines call for the tightest control, with two-hour readings below 140 mg/dl. The Joslin Diabetes Center and the American Diabetes Association suggest postmeal readings below 180 mg/dl.

“Postprandial goals are somewhat controversial,” Dr. Ganda says. “We haven’t really looked at this as a predictor of complications. Most of the research we have is based on HbA1c numbers, not postmeal readings. But, in my experience, to get an HbA1c result below 6.5 percent, your fasting blood sugar levels need to routinely be below 110 mg/dl, and your two-hour readings need to be less than 140 mg/dl. Unless you do that, you won’t be able to reach that goal.”


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