Glucose Tests

The fasting blood glucose level (collected after an 8 to 10 hr fast) is used to screen for and diagnose diabetes. An oral glucose tolerance test (OGTT / GTT) may also be used to diagnose diabetes. To be certain of a diagnosis of diabetes two tests (either the fasting glucose or the OGTT) should be done at different times. The OGTT involves a fasting glucose measurement, followed by the patient drinking a glucose drink to 'challenge' their system, followed by another glucose test two hours later.

Gestational diabetes is a temporary type of hyperglycaemia seen in some pregnant women, usually late in their pregnancy. Almost all pregnant women are screened for gestational diabetes between their 24th and 28th week of pregnancy using a test for glucose in the urine. If glucose is detected in the urine, they are considered at risk of developing gestational diabetes and they will undergo further testing.

Diabetics must monitor their own blood glucose levels, often several times a day, to determine how far above or below normal their glucose is and to determine what oral medications or insulin injections they may need. This is usually done by placing a drop of blood from a finger prick onto a plastic indicator strip and then inserting the strip into a glucose meter, a small machine that provides a digital readout of the blood glucose.

In those with suspected hypoglycaemia, glucose levels are used to help confirm a diagnosis.

The urine glucose is seldom requested by itself. At one time, it was used to monitor diabetics, but it has been largely replaced by the more sensitive and “real time” blood glucose. The urine glucose is, however, one of the substances measured when a urinalysis is performed. A urinalysis may be done as part of a examination or antenatal appointment, when a doctor suspects that a patient may have a urinary tract infection, or for a variety of other reasons. The doctor may follow a raised urine glucose test with blood glucose testing.

The test may be used as part of a routine examination especially in those people at high risk of developing diabetes - those with a family history of diabetes, those who are overweight and those who are more than 45 years old.

The glucose test may also be used to help diagnose diabetes when someone has symptoms of hyperglycaemia such as:

• Increased thirst
• Increased urination
• Urinary tract infections
• Tiredness
• Blurred vision
• Slow-healing infections

Glucose may also be tested when a person has symptoms of hypoglycaemia, such as:

• Sweating
• Hunger
• Trembling
• Anxiety
• Confusion
• Blurred Vision

Glucose testing is also done in emergency settings to determine if low or high glucose is contributing to symptoms such as fainting and unconsciousness.

If a patient has impaired glucose tolerance their fasting glucose or OGTT levels are higher than normal but not high enough to be diagnosed as a definite diabetes, in this situation, their doctor will request a glucose at regular intervals to monitor their progress. With known diabetics, doctors will use glucose levels in conjunction with other tests such as haemoglobin A1c (HbA1C) to monitor glucose control over a period of time.  Occasionally, a blood glucose level may be requested with insulin and C-peptide to monitor insulin.

Diabetics will self-check their glucose, once or several times a day, to monitor glucose levels and to determine treatment options.

Pregnant women are usually screened for gestational diabetes late in their pregnancies, unless they have had symptoms earlier or have had gestational diabetes with a previous child. When a woman has gestational diabetes, her doctor will usually request glucose levels throughout the rest of her pregnancy and after delivery to monitor her condition.

High levels of glucose most frequently indicate diabetes but many other diseases and conditions can also cause raised glucose. The following information summarizes the meaning of the test results.

Fasting Blood Glucose

Glucose Level	Indication
From 3.6 to 6.0 mmol/L	Normal fasting glucose
From 6.1 to 6.9 mmol/L	Impaired fasting glucose
7.0 mmol/L and above	Probable diabetes

Oral Glucose Tolerance Test (OGTT)

Sample taken 2 hours after a 75-gram glucose drink.

Glucose Level	Indication
Less than 7.8 mmol/L	Normal glucose tolerance
From 7.8 to 11.1 mmol/L	Impaired glucose tolerance
Over 11.1 mmol/L	Probable diabetes

Some of the other diseases and conditions that can result in elevated glucose levels include:

• Acromegaly
• Acute stress (response to trauma, heart attack, and stroke for instance)
• Long-term kidney disease
• Cushing's syndrome
• Drugs, including: corticosteroids, tricyclic antidepressants, diuretics, adrenaline, oestrogens (birth control pills and hormone replacement therapy [HRT]), lithium, phenytoin (Dilantin), aspirin
• Excessive food intake
• Hyperthyroidism
• Pancreatic cancer
• Pancreatitis

Moderately increased levels may be seen with impaired glucose tolerance. This condition, if left un-addressed, can lead to type 2 diabetes.

Low glucose levels (hypoglycaemia) are also seen with:

• Adrenal disease (Addison's disease)
• Drinking alcohol
• Drugs, such as: paracetamol and anabolic steroids
• Extensive liver disease
• Hypopituitarism
• Hypothyroidism
• Insulin overdose
• Insulinomas (insulin-producing pancreatic tumours)
• Starvation

Hypoglycaemia is characterised by a drop in blood glucose to a level where first it causes nervous system symptoms (sweating, palpitations, hunger, trembling, and anxiety), then begins to affect the brain (causing confusion, hallucinations, blurred vision, and sometimes even coma and death). An actual diagnosis of hypoglycaemia requires satisfying the following three criteria:

• Documented low glucose levels (less than 2.5 mmol/L)
• Symptoms of hypoglycaemia
• Reversal of the symptoms when blood glucose levels are returned to normal.

In some people with symptoms of low blood glucose, dietary changes such as eating frequent small meals and several snacks a day and choosing complex carbohydrates over simple sugars may be enough to help. Those with fasting hypoglycaemia may require IV (intravenous) glucose, if dietary measures are insufficient.