Patient information Leaflet- fasting glucose and lipid studies (cholesterol)
Fasting blood sugar and cholesterol levels are often requested by a doctor, as part of an overall cardiovascular disease risk check up, which would usually include a blood pressure check and other measurements. This is particularly the case for people who have a strong family history of either condition, or who have additional risk factors such as smoking, sedentary lifestyle or obesity. Diabetes and cardiovascular disease often occur in the same individuals.
Blood Glucose Tests
What is a fasting blood glucose test?
Blood glucose tests are also known as “blood sugar” tests. Glucose is a sugar that provides energy for your body. A blood glucose test measures the amount of glucose in your blood, and is generally taken at a pathology collection centre.
A blood glucose test may be done at a random time, without any special preparation (this is called a random or non-fasting blood glucose test). It can also be measured after you have fasted (not eaten for several hours)- i.e. a fasting blood glucose test.
Blood glucose may also be measured several times across a number of hours, as part of an oral glucose tolerance test (OGTT), which may be used to diagnose diabetes or “prediabetes”.
When is a blood glucose test recommended?
A blood glucose test is usually used to assess a person for diabetes, for example if they have symptoms of diabetes, risk factors for developing diabetes, or have had other tests that suggest diabetes could be present.
Symptoms of Type 1 Diabetes include increased thirst, passing a lot of urine, increased hunger, fatigue, unexpected weight loss, blurred vision, feeling irritable or other mood changes.
Symptoms of Type 2 Diabetes may be similar to the symptoms found in Type 1 diabetes, but often arise more gradually. Type 2 may also present with complications such as slow healing of cuts and wounds, increased occurrence of infections, or nerve damage such as numbness, pins and needles or pain in the hands or feet.
A test known as HBA1C is often also arranged to determine a person’s longer term glucose levels.
Sometimes if a person is suspected of having low blood sugar (hypoglycaemia), a fasting blood glucose may be arranged.
How should I prepare for a blood glucose test?
For a fasting blood glucose test, you should not eat anything for 8 to 12 hours before the test. You can drink water, but no other fluids. Drinking water and being well hydrated before your blood test can make it easier to draw blood.
Blood glucose tests are usually done at a pathology collection centre. Blood is drawn from a vein in your arm, and is then sent to a laboratory for testing.
What is an oral glucose tolerance test (OGTT)?
An oral glucose tolerance test (OGTT) measures how your body responds to glucose, and is sometimes used to assess a person for type 2 diabetes and pre-diabetes. It involves having a fasting glucose level, then having a sugary drink, and repeated blood tests over 1-2 hours.
Pre-diabetes is when blood glucose levels are higher than normal, but not high enough to officially diagnose Type 2 diabetes.
OGTTs are also frequently performed to check for gestational diabetes, in pregnancy.
What do my blood glucose test results mean?
High blood glucose is usually caused by diabetes, pre-diabetes or gestational diabetes. But there are also some other conditions that can cause high and low blood glucose levels. If your result shows a high blood glucose level, your doctor may suggest repeating the test and having other tests. Your doctor will look at your test results in the context of your symptoms and overall health- different levels may mean different things for different people.
According to the Royal College of Pathologists of Australasia:
“ in a patient with symptoms suggestive of diabetes mellitus, the finding of a fasting plasma glucose of >7.0 mmol/L, or a plasma glucose of >11.1 mmol/L at least 2 h following a meal, is diagnostic of diabetes mellitus. The finding of either of these levels on two occasions, even in the absence of symptoms, is also diagnostic of diabetes mellitus.
In patients with fasting plasma glucose levels between 5.5-6.9 mmol/L or random plasma glucose levels between 7.8-11.0 mmol/L, an oral glucose tolerance test should be performed if the patient is at high risk for diabetes.
Irrespective of any GTT results, a fasting plasma glucose 6.1-6.9 mmol/L indicates impaired fasting glucose.
Fasting plasma glucose levels < 5.5 mmol/L and/or random levels < 7.8 mmol/L make diabetes mellitus unlikely, and a GTT is not indicated”.
Fasting Cholesterol or “Lipid” blood tests
What is a fasting cholesterol (lipid) test?
A cholesterol (or lipid profile) test looks at the levels of cholesterol and other fats in your bloodstream. Cholesterol and lipids are fat-like substances in the body.
A lipid profile blood test measures:
- total cholesterol- the total level of cholesterol in your blood
- HDL-cholesterol- high-density cholesterol, often referred to as “good cholesterol”
- LDL-cholesterol- low-density cholesterol, often known as “bad” cholesterol
- Triglycerides- another type of fat in the body
LDL cholesterol is often referred to as “bad cholesterol” because it can build up in the walls of your blood vessels, increasing the risk of heart disease, vascular disease and stroke over time. High triglyceride levels can also increase your risk of cardiovascular disease.
HDL cholesterol is referred to as “good cholesterol” because it is involved in removing excess cholesterol from your body.
When is a fasting cholesterol test recommended?
You might be recommended to have this test as part of an assessment for cardiovascular disease. It is usually recommended every 5 years for people who are otherwise well, starting from 45 years of age (35 years for Aboriginal or Torres Strait Islander people).
For people with health issues such as diabetes, chronic kidney disease, heart disease, stroke or high blood pressure (hypertension), annual testing may be advised. Regular cholesterol tests may also be advised if you are on medication for high cholesterol, to monitor your response.
What do the results of my cholesterol test mean?
The results of your lipid profile test will need to be discussed with your doctor, as there are different guidelines for target cholesterol levels in different people, depending on their health issues and other factors.
Cholesterol and lipid levels are just one element taken into consideration when assessing a person’s risk of cardiovascular disease. Smoking status, age, blood pressure, family history, diet and lifestyle are some other important issues.
The National Heart Foundation of Australia recommends the following targets for lipid levels. These are guidelines- the decision regarding the target is an individual one, ideally made with your regular doctor:
- Total cholesterol <4.0mmol/L
- HDL cholesterol >1.0mmol/L
- LDL cholesterol < 2.0mmol/L
- Non-HDL cholesterol <2.5mmol/L
- Triglycerides <2.0mmol/L
The first step in managing high cholesterol is a change in lifestyle, for example a diet low in saturated fat, and increasing exercise. A dietitian or exercise physiologist or personal trainer may be able to support you and add some accountability.
When is treatment needed for high cholesterol?
The following groups are recommended for treatment by the Royal Australian College of General Practitioners. However, sometimes treatment may be recommended for individuals, even if they do not fall into any of the categories below. In addition, some people may decide, in consultation with their doctor, to focus purely on lifestyle changes.
- Patients with a cardiovascular risk >15%
- Patients with pre-existing cardiovascular disease
- Patients aged >60 with diabetes, or with diabetes-related kidney disease
- Patients with chronic kidney disease
- Patients with moderate or severe hypertension (high blood pressure)
- Patients with total cholesterol greater than 7.5mmol/L
- People of Aboriginal or Torres Strait Islander background aged >74
- Patients with familial hypercholesterolaemia (a genetic condition)
Further Resources
Health Direct- blood glucose tests
Health Direct- lipids and cholesterol tests
Pathology Tests Explained- Lipids
Royal College of Pathologists of Australasia- fasting glucose
