—Steve Parker, M.D.
* * *
Physicians focus so much on disease that we sometimes lose sight of what’s healthy and normal. For instance, the American Diabetes Association defines “tight” control of diabetes to include sugar levels as high as 179 mg/dl (9.94 mmol/l) when measured two hours after a meal. In contrast, young adults without diabetes two hours after a meal are usually in the range of 90 to 110 mg/dl (5.00–6.11 mmol/l).
What Is a Normal Blood Sugar Level?
The following numbers refer to average blood sugar (glucose) levels in venous plasma, as measured in a lab. Portable home glucose meters measure sugar in capillary whole blood. Many, but not all, meters in 2010 are calibrated to compare directly to venous plasma levels.
Fasting blood sugar after a night of sleep and before breakfast: 85 mg/dl (4.72 mmol/l)
One hour after a meal: 110 mg/dl (6.11 mmol/l)
Two hours after a meal: 95 mg/dl (5.28 mmol/l)
Five hours after a meal: 85 mg/dl (4.72 mmol/l)
(The aforementioned meal derives 50–55% of its energy from carbohydrate)
♦ ♦ ♦
Ranges of blood sugar for young healthy non-diabetic adults:
Fasting blood sugar: 70–90 mg/dl (3.89–5.00 mmol/l)
One hour after a typical meal: 90–125 mg/dl (5.00–6.94 mmol/l)
Two hours after a typical meal: 90–110 mg/dl (5.00–6.11 mmol/l)
Five hours after a typical meal: 70–90 mg/dl (3.89–5.00 mmol/l)
Blood sugars tend to be a bit lower in pregnant women.
♦ ♦ ♦
What Level of Blood Sugar Defines Diabetes and Prediabetes?
According to the 2007 guidelines issued by the American Association of Clinical Endocrinologists:
Prediabetes: (or impaired fasting glucose): fasting blood sugar 100–125 mg/dl (5.56–6.94 mmol/l)
Prediabetes: (or impaired glucose tolerance): blood sugar 140–199 mg/dl (7.78–11.06 mmol/l) two hours after ingesting 75 grams of glucose
Diabetes: fasting blood sugar 126 mg/dl (7 mmol/l) or greater
Diabetes: blood sugar 200 mg/dl (11.11 mmol/l) or greater two hours after ingesting 75 grams of glucose
Diabetes: random (“casual”) blood sugar 200 mg/dl (11.11 mmol/l) or greater, plus symptoms of diabetes
If there’s any doubt about the diagnosis, testing should be repeated on a subsequent day.
Compared to impaired fasting glucose, impaired glucose tolerance may be a better predictor of cardiovascular disease and death. So some researchers and clinicians focus on preventing high blood sugar swings after meals. The problem with prediabetes, which causes no symptoms early on, is that one of every four cases progresses to full-blown diabetes over the next 3–5 years.
The numbers above do not apply to pregnant women. Five percent of pregant women develop gestational diabetes that goes away soon after delivery.
What Level of Hemoglobin A1c Defines Diabetes?
Another way to consider normal and abnormal blood sugar levels is to look at a blood test called hemoglobin A1c, which is an indicator of average blood sugar readings over the prior three months. The average healthy non-diabetic adult hemoglobin A1c is 5% and translates into an average blood sugar of 100 mg/dl (5.56 mmol/l). This will vary a bit from lab to lab. Most healthy non-diabetics would be under 5.7%.
In December, 2009, the American Diabetes Association established a hemoglobin A1c criterion for the diagnosis of diabetes: 6.5% or higher. Diagnosis of prediabetes involves hemoglobin A1c in the range of 5.7 to 6.4%. The aforementioned blood sugar criteria can also be used.
What Are Blood Sugar Goals During Treatment For Diabetes?
The 2007 guidelines of the American Association of Clinical Endocrinologists “encourage patients [both type 1 and 2] to achieve glycemic [blood sugar] levels as near normal as possible without inducing hypoglycemia [low blood sugar].” Specifically:
Fasting blood sugar: <110 mg/dl (6.11 mmol/l)
Two hours after a meal: <140 mg/dl (7.78 mmol/l)
Hemoglobin A1c: 6.5% or less
The American Diabetes Association recommends normal or near-normal blood sugar levels, and defines “tight control” as:
1) pre-meal and fasting glucose levels of 70–130 mg/dl (3.89–7.22 mmol/l)
2) sugars under 180 mg/dl (10.00 mmol/l) two hours after start of a meal
3) hemoglobin A1c under 7%.
A hemoglobin A1c of 7% is equivalent to average blood sugar levels of 160 mg/dl (8.89 mmol/l). Hemogobin A1c of 6% equals, roughly, average blood sugar levels of 130 mg/dl (7.22 mmol/l). But remember, healthy non-diabetics spend most of their day under 100 mg/dl (5.56 mmol/l) and have hemoglobin A1c’s around 5%.
Diabetic experts actively debate how tightly we should control blood sugar levels. For instance, Dr. Richard K. Bernstein—a type 1 diabetic himself—recommends keeping blood sugar levels under 90 mg/dl (5.00 mmol/l) almost all the time. If it exceeds 95 mg/dl (5.28 mmol/l) after a meal, then a change in medication or meal is in order, he says.
Here’s the over-simplified “tight control” debate. On one hand, tight control helps prevent and may reverse some of the devastating consequences of diabetes. On the other hand, tight control in diabetics on insulin and certain other diabetic medications may raise the risk of life-threatening hypoglycemia and may shorten lifespan in other ways.
Blood Sugar Goals For My Personal Diabetic And Prediabetic Patients
Ideally, normal glucose levels before and after meals, with normal hemoglobin A1c.
Realistically, these are acceptable fall-back positions:
Fasting blood sugar: under 100 mg/dl (5.56 mmol/l)
One hour after meals: under 150 mg/dl (8.33 mmol/l)
Two hours after meals: under 130 mg/dl (7.22mmol/l)
Hemoglobin A1c: 6% or less
Treatment options for those not at goal include diet modification, weight loss, exercise, and medications. Admittedly, those goals are not acceptable or achievable by everyone with diabetes. Future studies may prove that such strict goals are not necessary to avoid the complications and premature death suffered by people with diabetes. Tight control may be less important for elderly diabetics over 65–70. But for now, if I were a young or middle-aged diabetic I’d shoot for the goals above.
The gold standard for measuring glucose is a large chemistry analyzer in a lab, which measures values in plasma obtained from a vein with a needle. The glucose level in capillary whole blood, obtained via fingerprick and analyzed on a portable/home glucose monitor, is a different value, often 5–10 mg/dl higher than venous glucose. As of 2010, a majority of home glucose monitors, but not all, are calibrated so as to be directly comparable to venous plasma glucose readings. Read your monitor’s paperwork to find out about your device.
Portable fingerstick glucose meters are not as accurate and as you might expect. If your actual glucose level is 100 mg/dl, the meter may report it as 80 or 120 or anywhere in between, for example. The meters tend to be less accurate at glucose values over 200 mg/dl. Some devices are definitely more accurate than others. Research the available devices before you acquire one.
Outside the U.S., glucose is usually reported in units of mmol/l (millimoles per liter). One mmol/l = 18 mg/dl. To convert mg/dl to mmol/l, divide by 18 or multiply by 0.055.
Last updated May2, 2016