Blood glucose

What is being tested?
Glucose is a simple sugar that is the body’s main source of energy. The carbohydrates we eat are broken down into glucose (and a few other simple sugars), absorbed in the small intestine and circulated around the body. Most of the body’s cells need glucose to produce energy; brain and nerve cells not only depend on glucose for energy, they can only function when blood glucose levels remain above a certain level.
The body’s use of glucose depends on the availability of insulin, a hormone produced by the pancreas. Insulin acts like a traffic controller, moving glucose into the body’s cells and directing the body to store excess glucose as glycogen (for short-term storage) and/or as triglycerides in fat cells. It is not possible to survive without glucose or insulin, and they must be kept in balance.

Normally blood glucose levels rise slightly after a meal, and insulin is released to lower them, with the amount of insulin released matching the size and content of the meal. If blood glucose levels fall too low, as can happen between meals or after intense exercise, glucagon (another pancreatic hormone) is released to tell the liver to turn some glycogen into glucose, raising blood glucose levels. If the glucose/insulin feedback mechanism is working properly, the amount of glucose in the blood remains fairly stable. If the balance is disrupted and blood glucose levels rise, the body tries to restore the balance by increasing insulin production and excreting glucose in the urine.

Severe, acute hyperglycaemia or hypoglycaemia can be life-threatening, causing organ damage, brain damage, coma and, in extreme cases, death. Chronically high glucose levels can cause progressive damage to body organs such as the kidneys, eyes, heart and blood vessels. Chronic hypoglycaemia can lead to brain and nerve damage.

Some women develop hyperglycaemia during pregnancy, and this can lead to gestational diabetes. If untreated, this can cause mothers to give birth to large babies who may have low glucose levels. Women who have had gestational diabetes may or may not go on to develop diabetes.

How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?

How is it used?
The blood glucose test is requested to determine the exact amount of glucose in the blood at the time of sampling. It is used to assess hyperglycaemia and hypoglycaemia and to guide diagnosis. Blood glucose can be measured fasting (a sample taken after 8-10 hours without food), at random (at any time), after a meal (post-prandial) and/or after taking glucose as a tolerance test (OGTT/GTT). An OGTT is a series of blood glucose tests. A fasting sample is taken; the patient then drinks a standard amount of glucose solution to challenge the system. This is followed by one or more further tests at set intervals to measure glucose levels each time. The OGTT may be requested to help diagnose diabetes and as a follow-up to a high blood glucose.
The American Diabetes Association recommends either fasting glucose or the OGTT to diagnose diabetes, but advises that the test should be repeated on a different day to confirm the diagnosis.

Most pregnant women are tested for gestational diabetes, a temporary form of hyperglycaemia, between the 24th and 28th weeks of pregnancy, using a version of the OGTT, 1 hour after a glucose challenge. If fasting glucose or random glucose is above the value used to diagnose diabetes in women who are not pregnant, the woman has gestational diabetes and neither the screening nor the glucose tolerance test is needed. If the 1-hour level is above the set value, a longer OGTT is used to clarify the patient’s status.

People with diabetes need to monitor their blood glucose levels, often several times a day, to know how high or low their glucose is and what medicine, taken by mouth or as insulin, they may need. This is normally done by placing a drop of blood from a finger-prick on a glucose test strip and then inserting the strip into a glucose meter, a small device that gives a digital reading of the glucose level.

In people with suspected hypoglycaemia, glucose levels are used as part of “Whipple’s triad” to confirm the diagnosis (see the section “Is there anything else I should know?”)

Urine glucose is rarely tested on its own. It was once used to monitor people with diabetes, but has largely been replaced by more sensitive real-time blood glucose testing. Urine glucose is, however, one of the substances tested for when urinalysis is requested. Urinalysis may be done routinely, when the doctor suspects the patient may have a urinary tract infection, or for other reasons. The doctor may follow up a high urine glucose concentration with a blood glucose test.

When is it requested?
A glucose test can be used to screen people without symptoms for diabetes and prediabetes, since diabetes is a common disease that begins with few symptoms. Glucose screening may take place during a public health programme or as part of a workplace programme. It may also be requested for a patient during a routine check-up. Screening is very important in people at high risk of developing diabetes, such as those with a family history of diabetes, those who are overweight and those over 40-45.
A glucose test may be requested to help diagnose diabetes when a person has symptoms of hyperglycaemia, such as:

• increased thirst
• increased need to pass urine
• tiredness
• blurred vision
• infections that are slow to heal

or symptoms of hypoglycaemia, such as:

• sweating
• hunger
• tremor
• anxiety
• confusion
• blurred vision

The glucose test is also carried out in emergencies to find out whether a rise or fall in glucose is linked to symptoms such as weakness or loss of consciousness. If a patient has prediabetes (characterised by fasting or OGTT levels that are higher than normal but lower than those defining diabetes), the doctor will request glucose levels at regular intervals to monitor the patient’s condition. Once diabetes has been diagnosed, doctors will request glucose levels together with other tests such as haemoglobin A1c to monitor glucose concentrations over time. Occasionally a glucose level may be requested together with insulin and C-peptide tests to monitor insulin production.

People with diabetes may be asked to monitor their own glucose one or more times a day, to follow their glucose levels and adjust their treatment as prescribed by the doctor.

Pregnant women are generally tested for gestational diabetes late in pregnancy, unless they have early symptoms or have had gestational diabetes before. When a woman has gestational diabetes, her doctor will usually request glucose levels throughout the pregnancy and after delivery to monitor her health.

What does the test result mean?
High glucose levels most often indicate diabetes, but many other diseases and conditions can cause high glucose levels. The following information summarises the meaning of the test results. It is based on the clinical practice recommendations of the American Diabetes Association.

Some other diseases and conditions that can cause high glucose levels include:

• acromegaly
• acute stress (response to injury, heart attack and stroke, for example)
• chronic kidney disease
• Cushing’s syndrome
• medicines, including corticosteroids, tricyclic antidepressants, diuretics, epinephrine, oestrogens (birth control pills, hormone replacement), lithium, phenytoin (Dilantin) and salicylates
• excessive food intake
• hyperthyroidism
• pancreatic cancer
• pancreatitis

Undetectable amounts of glucose in urine are considered normal. Anything that raises blood glucose levels can potentially raise urine glucose levels. Raised urine glucose levels can be due to medicines, such as oestrogens and chloral hydrate, and to some forms of kidney disease.
Moderately raised levels may be seen as prediabetes. If left untreated, this condition often leads to type 2 diabetes.

Low glucose levels (hypoglycaemia) are also associated with:

• adrenal insufficiency
• alcohol intake
• medicines, such as paracetamol (acetaminophen) and anabolic steroids
• liver disease
• hypopituitarism
• hypothyroidism
• excess insulin
• insulinomas (insulin-producing tumours of the pancreas)
• starvation

Is there anything else I should know?
Hypoglycaemia is characterised by a fall in blood glucose to levels that first cause nervous system symptoms (sweating, palpitations, hunger, trembling and anxiety) and then begin to affect the brain (causing confusion, hallucinations, blurred vision and sometimes coma and death). A diagnosis of hypoglycaemia requires “Whipple’s triad” to be satisfied. These three criteria include:

• documented low glucose levels (less than 40 mg/dl (2.2 mmol/L)), often tested together with insulin levels and sometimes with C-peptide levels
• symptoms of hypoglycaemia
• relief of symptoms when blood glucose levels return to normal

Primary hypoglycaemia is rare and is often diagnosed in childhood. People can have symptoms of hypoglycaemia without actually having low blood glucose concentrations. In these cases, dietary changes, such as eating small, frequent meals and several snacks a day and choosing complex carbohydrates over simple sugars, may be enough to reduce the symptoms. People with fasting hypoglycaemia may need glucose (intravenously) if dietary measures are not enough

1. Can I measure my own blood glucose levels at home?
2. Can glucose be tested in urine instead of blood?
3. What are the most common treatments for diabetes?
4. How can a diabetes educator help me?

1. Can I measure my own blood glucose levels at home?
If you do not have diabetes or prediabetes, there is no reason to measure your glucose levels at home. The screening done as part of your health checks should be enough.

If you have been diagnosed with diabetes, however, your doctor or endocrinologist will recommend a glucose monitoring device (a glucose meter, or one of the newer methods that use a very small amount of blood or test the interstitial fluid, the fluid between cells, to measure glucose). You will be given guidelines on when to check your blood glucose at different times and on different days. By checking your glucose regularly, you can find out whether the diet and medicine plan you are following is adequate.

2. Can glucose be tested in urine instead of blood?
Not in most cases. Glucose will be high in the urine only if blood levels are high enough for the body to “offload” the excess into the urine, or if there is some degree of kidney damage and glucose is lost in the urine. Urine glucose is, however, sometimes used as a rough indicator of high glucose levels, and the urine dipstick that measures glucose is occasionally useful for detecting protein and ketones in the urine.

3. What are the most common treatments for diabetes?
For type 2 diabetes, the most common form of diabetes, losing excess weight, eating a healthy diet high in fibre and low in carbohydrates, and taking regular exercise may be enough to lower blood glucose levels. In many cases, however, medicines that increase insulin secretion and sensitivity are needed to reach the desired glucose level. With type 1 diabetes (and with type 2 diabetes that does not respond well enough to medicines), insulin injections are needed several times a day.

4. How can a diabetes educator help me?
If you have diabetes, a diabetes educator (often a specialist nurse) should make sure you know how to:

– Plan your meals (a dietitian can also help). Diet is extremely important in minimising swings in blood glucose levels
– Recognise and deal with high and low glucose levels
– Test and record your glucose values
– Adjust your medicines
– Take insulin (which types, in what amounts, for best use)
– Use your medicines when you are ill
– Check your feet, skin and eyes to catch problems early
– Buy diabetic supplies and store them properly