7 Important Numbers and Tests People with Diabetes Need to Know

Here at DiabetesCare.net, we are always happy to answer your questions about diabetes. Some of the most frequent questions we answer are:

• What is blood glucose?
• What do the terms fasting blood sugar and random blood sugar mean?
• How are diabetes and pre-diabetes diagnosed?
• If I have diabetes, what is the significance of pre-prandial and postprandial plasma glucose?
• What should my blood glucose (blood sugar) and hemoglobin A1C numbers be?
• How many grams of carbohydrate do I need?
• Is there a healthy recommendation for percentage of calories as carbohydrates?

Here are the answers to these questions!

Blood Glucose: Blood glucose is sometimes referred to as blood sugar. Our body breaks down the carbohydrates we eat into glucose. We need glucose to to supply energy to our cells. The National Academy of Sciences Institute of Medicine Food and Nutrition Board recommends at least or a minimum of 130 grams of carbohydrate per day for people over the age of one year. The minimum for pregnancy is 175 grams and the minimum for breast feeding is 210 grams. These values were set based on the fact that carbohydrate is the primary source of energy for the brain. (1) It is recommended by the Food and Nutrition Board that we eat 45-65 percent of all of our calories as carbohydrate. This number is the Acceptable Macronutrient distribution range (AMDR) for carbohydrates.  (For your information, The AMDR for protein is 10-35 percent of energy and fat is 20-35 percent of energy with a note to limit saturated and trans-fats). There are also specific recommendations that are based on weight for non-pregnant adults. The range of carbohydrate needed varies between 5-12 grams of carbohydrate per kilogram of body weight. (2)

As food that contains carbohydrates is broken down by digestion when we eat, our blood glucose will rise as it enters our blood stream. Normally blood glucose is consumed by our cells very quickly and excess glucose is stored as fat. If this does not happen and there is too much glucose in the blood, pre-diabetes or diabetes may be diagnosed. Blood glucose values should be tested and then repeated on a second separate day for accuracy if there is a questionable diagnosis. Testing may include hemoglobin A1C levels. Diabetes is a serious disease that can cause damage to our organs, including our eyes, feet, kidneys, and blood vessels. (3) It is important to follow the advice of your medical team to keep your blood glucose under control.

The 7 Important Numbers People with Diabetes Need to Know

1. What is Fasting Plasma Glucose (FPG) or Fasting Blood Sugar (FBS)?

Fasting plasma glucose is the amount of blood glucose present in the blood after fasting (not eating anything with calories) for at least eight hours. It represents the amount of glucose present for that one moment in time. When FPG is drawn for diagnosing purposes, the following values are most often used:

Normal: FPG between 70- 100 mg/dl (4)
Pre-diabetes: FPG 100 mg/dL (5.6 mmol/L) to 125 mg/dL (6.9 mmol/L) (5)
Diabetes: FPG greater 126 mg/dL (7.0 mmol/L) (5)

2. What is random blood sugar?

This test is sometimes done to diagnose diabetes with classic symptoms of hyperglycemia (high blood sugar) or hyperglycemic crisis. A person can have this blood work taken at anytime, which means the person does not need to be fasting.

Diabetes: A random plasma glucose greater or equal to 200 mg/dL (11.1 mmol/L). (5)

3. What is a two-hour plasma glucose or Oral Glucose Tolerance Test (OGTT)?

This test is sometimes used to confirm a diagnosis of diabetes. One needs to fast for at least eight hours before this test. After arriving at the lab, the person will be given a drink containing a mixture of water and 75 grams of anhydrous glucose.  The blood glucose will be measured after two hours have elapsed. If positive results are measured, the test should be repeated for confirmation if there is an absence of unequivocal hyperglycemia. (6)

Normal: Less than or equal to 139 mg/dl (7)
Pre-diabetes:  Two-hour plasma glucose in the 75-g OGTT 140 mg/dL (7.8 mmol/L) to 199 mg/dL (11.0 mmol/L) (5, 7)
Diabetes: Two-hour plasma glucose greater or equal to 200 mg/dL (11.1 mmol/L) (5, 7)

When conversion is needed for blood glucose information from mg/dl to mmol/l or the opposite, go here.

4. What is Hemoglobin A1C ( or A1C)? Is it used to diagnose diabetes and if so, what numbers are used? What should my target be if I already have diabetes?

Hemoglobin is found in red blood cells and carries oxygen to the cells of our body and carbon dioxide back from cells to our lungs. Glucose (sugar) binds to the A1C portion of our hemoglobin. When glucose increases in the bloodstream, more will be attached to hemoglobin.  A Hemoglobin A1C or glycated hemoglobin A1C test measures the percentage of total hemoglobin in our red blood cells that is bound by glucose. (8)  When glucose attaches to the molecule, it stays attached for the life of the cell which is approximately three months. The hemoglobin A1C test indicates the blood glucose reading for this time period. It is interesting to note that the glucose levels in the blood for the last 30 days before the hemoglobin A1C level is taken contributes substantially more to the value than earlier glucose levels. (9) The following values are used for the diagnosis of diabetes:

Normal: 5.6 percent or less (10)
Pre-diabetes: A1C 5.7–6.4 percent (5, 10)
Diabetes: A1C equal or greater than 6.5 percent (5, 10)

The American Association of Clinical Endocrinologists recommends the following values for the diagnosis of diabetes using A1C:

Normal: AIC less or equal to 5.4 percent (7)
Pre-diabetes:  A1C  5.5-6.4 percent (7)
Diabetes– A1C 6.5 percent or higher (7)

The American Diabetes Association recommends this test be performed in a laboratory that is certified using the National Glycohemoglobin Standardization Program (NGSP).  For a list of certified laboratories, go here.

The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) recommends the use of SI (Système International) to report A1C. Units reported are  in mmol/mol. (11)  NGSP has a conversion table available to convert A1c values from (mmol/mol) to mg/dl or vice versa, here.

A1C values are important to monitor. Target values for A1C will depend on a person’s medical condition, if they are prone to severe hypoglycemia, life expectancy and ability to maintain blood glucose goals. The targets should be agreed upon with your physician. (12)

For many people a target goal of 6.5 to 7 percent is recommended. Studies have shown that this will reduce the risk of diabetes microvascular complications. (13)

It is interesting to note that in people with diabetes who are not under control, a one point reduction in A1C lowers the risk of complications such as eye, kidney, and nerve disease by 40 percent. (14)

5. What is Estimated Average Glucose (eAG)?

This value is calculated from the A1C levels. This number is a conversion of A1C percentage values into milligrams per deciliter (mg/dL). This value helps explain blood sugar values to many patients. (15) A conversion chart is available here.

6. What is the difference between gestational diabetes vs. diabetes diagnosed at the first prenatal visit? What blood glucose values are used to diagnose gestational diabetes?

If a woman is screened at her first pre-natal visit and diabetes is diagnosed, she will be diagnosed with diabetes not gestational diabetes. This is because it is assumed she had diabetes already before the pregnancy. Gestational diabetes is usually diagnosed at 24-28 weeks of pregnancy. This type of diabetes did not occur before the pregnancy.  Usually an oral glucose tolerance test (OGTT) is used for diagnosis. The procedure for this is usually the same as the OGTT described above except for the following: When the woman arrives for the test a fasting plasma glucose test will be taken. She will then drink a solution made with 75 grams of glucose. Plasma glucose levels will be taken at one and two hours after her drink.

Gestational diabetes is diagnosed if any of the plasma glucose values are equal or higher than the following:

• Fasting greater or equal than 92 mg/dL (5.1 mmol/L) (16)
• One-hour: greater or equal than 180 mg/dL (10.0 mmol/L) (16)
•  Two-hour: 1 greater or equal than 153 mg/dL (8.5 mmol/L) (16)

Please ask your physician for blood sugar targets during this special time if you have type 1, type 2 or gestational diabetes while pregnant.

7. What should my target values be for blood glucose before and after a meal if I have the diagnosis of diabetes?

If you have diabetes, the following blood glucose values are often recommended as goals or target ranges. Blood glucose values need to be individualized. Ask your physician if you should strive for these values.

Pre-prandial plasma glucose (before eating): This blood glucose reading is taken before you have a meal. The American Diabetes Association recommends a value of 70-130 mg/dl for most non-pregnant adults. (17)

The American Association of Clinical Endocrinologists recommends a value for most non-pregnant adults of 110 mg/dl or less. (18)

Postprandial plasma glucose) (after eating): This value is taken one-two hours after the first bite of a meal. The American Diabetes Association recommends a value of less than 180 mg/dl for most non-pregnant adults. (17)

The American Association of Clinical Endocrinologists recommends a value for most non-pregnant adults of 140 mg/dl or less. (18)

We hope your questions about blood glucose values have been answered.  Please have a discussion with your physician to ask if these values are correct for you!

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