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Blood Glucose

Why is this test performed? Blood glucose is often measured as part of a group of tests to screen for diabetes. It is also used to monitor glucose levels in persons with diabetes.
How to prepare: Laboratory test
  • A blood sample will be drawn
  • Your physician may also order other tests:
    • Fasting is required for a minimum of 8 hours before the test
    • Ingestion of a special glucose solution
    • No special consideration with regards to food
      • Self-monitoring at home
      • The blood sample is generally taken from a finger prick
      • Time and frequency of sampling varies for each individual
    Diabetes screening levels: Levels that may be indicative of diabetes
    • Fasting blood sugar ≥ 7.0 mmol/L
    • Random blood sugar taken throughout the day ≥ 11.1 mmol/L
    Diabetes monitoring and management levels:
    • First thing in the morning and before meals: 4.0 to 7.0 mmol/L.
    • 2 hours after a meal: 5.0 to 10.0 mmol/L, in certain circumstances between 5.0 to 8.0 mmol/L.
    Related tests: This test can be ordered on its own or with complimentary tests. If monitoring a patient who is diabetic, the following tests may be requested: glycosylated hemoglobin , lipid profile (ex.: cholesterol , triglycerides ) and kidney function (ex.: serum creatinine , microalbuminuria ).

    General Information

    Glucose is an essential nutrient that provides energy for the proper functioning of the body. In fact, it is the body's key source of energy and the primary source of energy for the brain and nervous system. The relationship between our dietary intake, what is synthesized by the liver, the use of stores and what is excreted by the kidneys is what regulates blood glucose levels.

    What does an abnormal test result mean?

    If the result is too high
    This is usually a sign of diabetes.

      Symptoms of hyperglycemia
      • Increased thirst
      • Fatigue
      • Blurred vision
      • Slow-healing infections

    If the result is low
    A glucose level of 3.9 mmol/L or less is known as hypoglycemia. When left untreated, severe hypoglycemia can be life-threatening. Taking too much insulin or other diabetes medications, exercise, and not getting enough sugar to meet one's needs are among some of the most common causes of hypoglycemia. Drinking alcohol in the fasting state can also cause hypoglycemia.

      Symptoms of hypoglycemia
      • Excessive sweating
      • Trembling
      • Rapid heart beat
      • Dizziness
      • Confusion
      • Blurred vision
      • Anxiety

    Factors that can affect results

    Certain health conditions, as well as certain medications, can alter blood glucose levels.

    Factors that can lower blood glucose levels include:

    • Adrenal insufficiency
    • Excessive alcohol intake
    • Severe liver disease
    • Hypothyroidism
    • Starvation

    Factors that can increase blood glucose levels include:

    • Acute stress
    • Chronic kidney failure
    • Cushing's syndrome
    • Hyperthyroidism
    • Pancreatic cancer
    • Pancreatitis

    Medications that can increase blood glucose levels:

    • Beta-blockers (ex. metoprolol (Lopresor®))
    • Certain diuretics
    • Oral contraceptives
    • Corticosteroids (prednisone, cortisone)
    • Estrogen
    • Thyroid hormones (ex. levothyroxine (Synthroid®))
    • Lithium (Carbolith®)
    • Certain antipsychotics
    • Phenytoin (Dilantin®)

    What you need to know before the test

    Before going for blood tests, a procedure or other exam, it is best to always bring a list of all the drugs you take (prescription, OTC and natural health products). Unless told otherwise, you should take your medication as usual on the day of the test. When in doubt, ask your pharmacist for more information.

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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.

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