Blood sugar (laboratory)
Glucose is a kind of sugar used by the body as its main source of energy. It is obtained from the food we eat. Blood sugar testing measures sugar levels in the blood (glycemia). Insulin is a hormone produced in the pancreas that helps the cells use blood sugar. Our blood sugar levels increase slightly after we eat, and insulin ensures they don't get too high. Consistently high blood sugar can cause damage to the eyes, kidneys, nerves, and blood vessels.
| What is the purpose of this test? | A fasting blood sugar test may be requested as part of a routine examination, particularly in people at high risk of developing diabetes. The various blood sugar tests are used to:
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| How to prepare? |
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| Associated tests | Related tests include:
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| How it is done? | A blood sample is drawn, usually from a vein in the arm. |
| How long before I get the results? | Results are usually ready in a day. It may take longer to receive your results. |
Various tests can be performed to detect diabetes. Typical blood tests include fasting blood sugar test, glycated hemoglobin and Oral glucose tolerance test (OGTT). Random blood sugar testing may also be used. Normally, two blood tests with abnormal results are needed to establish a diagnosis of diabetes.
| Fasting blood sugar | Random blood sugar | |
|---|---|---|
| Normal | 4.0-6.0 mmol/L | 4.0-11 mmol/L |
| Prediabetes | 6.1-6.9 mmol/L | n/a |
| Diabetes | ≥ 7.0 mmol/L | ≥ 11.1 mmol/L |
In order to delay and even prevent the complications of diabetes, target values for glycated hemoglobin and blood sugar have been developed. These targets must be assessed for each individual diabetic, depending on a number of factors (e.g. age, sex, health condition). The following table shows target values for glycated hemoglobin for adults with diabetes.
| Fasting or pre-meal blood sugar levels | Blood sugar 2 hours after a meal | |
|---|---|---|
| Targets for achieving a glycated hemoglobin level ≤ 7.0% | 4.0-7.0 mmol/L | 5.0-10.0 mmol/L |
| Targets if glycated hemoglobin level ≤ 7.0% not achieved with the above values | 4.0-5.5 mmol/L | 5.0-8.0 mmol/L |
What does an abnormal test result mean?
High values of glycemia:
- May indicate diabetes or a risk of developing diabetes
- May indicate poor blood sugar control in a person with diabetes
- May indicate other conditions such as hyperthyroidism, or pancreatic disease
Low values of glycemia:
- May indicate hypoglycemia or a risk of hypoglycemia
- May indicate poor blood sugar control in a person with diabetes
- May indicate other conditions such as liver disease, kidney disease, or hypothyroidism
Medications that may affect test results
The use of certain medications can influence test results. Here are a few examples:
- Corticosteroids (e.g., prednisone)
- Tricyclic antidepressants
- Diuretics
- Adrenaline
- Estrogen
- Lithium
- Phenytoin
What you should know before going for this test
When you go in for a blood test or any other medical exam, it's always a good idea to bring a complete list of any prescriptions, over-the-counter medications, or natural health products you're taking. Unless otherwise advised, it's best to take your medications as usual on blood test days. If in doubt, don't hesitate to talk to your healthcare professional.
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The patient information leaflets are provided by Vigilance Santé Inc. This content is for information purposes only and does not in any manner whatsoever replace the opinion or advice of your health care professional. Always consult a health care professional before making a decision about your medication or treatment.