What are Blood Glucose Tests?
Blood glucose tests, also referred to as blood sugar tests, are simple procedures performed to measure the level of glucose in your blood. Glucose is a simple sugar that supplies energy for your body. However, too much or too little glucose in the blood can be a sign of a serious medical condition.
Blood glucose tests usually involve a blood draw from your vein in a laboratory setting, although blood from a finger prick may also be used to measure the blood glucose level. Healthcare providers usually employ blood glucose tests to screen for type 2 diabetes, which is a common medical condition.
Types of Blood Glucose Tests
There are two main types of blood glucose tests:
- Capillary blood glucose test: In this test, a healthcare professional will collect a drop of your blood, typically from a fingertip prick. This type of glucose test involves a test strip and glucometer (glucose meter), which show your blood sugar level within seconds of placing the drop of blood on the test strip.
- Venous (plasma) blood glucose test: In this test, a healthcare professional or a phlebotomist obtains a sample of blood from your vein (venipuncture). The sample is then sent to a lab for analysis where a lab technician prepares your sample and performs the test on machines known as analyzers. This type of glucose test is usually part of a blood panel, such as a basic metabolic panel.
Venous blood glucose tests are usually more accurate than capillary blood glucose tests.
Indications for Blood Glucose Tests
Blood glucose tests are usually indicated to check for signs of diabetes or to monitor people who already have diabetes.
Diabetes is a chronic metabolic disorder characterised by hyperglycemia or the presence of high sugar (glucose) levels in the blood. The level of glucose in the blood is regulated by the hormone insulin, which is produced by the pancreas. Diabetes occurs when either the pancreas does not produce sufficient insulin or when the body cannot effectively utilise the insulin it produces. Hyperglycemia is a common effect of uncontrolled diabetes and over time results in serious damage to many of the body's systems, typically the nerves and blood vessels.
Additional diabetes tests, such as the haemoglobin A1C (HbA1C) test, may be required if your physician thinks you may have diabetes.
Blood glucose tests may also be recommended if you have symptoms that may be associated with low blood glucose levels (hypoglycemia) or if you have a high risk of developing type 2 diabetes.
Preparation for Blood Glucose Tests
Preparation for blood glucose tests falls into several categories, including:
- Fasting
- Random (non-fasting)
- Oral glucose tolerance test (OGTT), a 2-hour test
- Post-prandial, meaning testing after having food or drink
Physicians use fasting, random, and OGTT tests to diagnose diabetes, whereas post-prandial tests can assist in determining how well an individual with diabetes is managing their blood sugar levels.
If your physician orders a fasting blood glucose test or an OGTT, you are required to fast (not eat or drink) for at least 8 hours prior to the test. Other blood glucose tests do not require any special preparations. Prior to the test, tell your physician about any medications you are taking, such as prescriptions, over-the-counter drugs, and herbal supplements. Certain medications can influence blood glucose levels. Your physician may ask you to stop taking a specific medication or alter the dosage of the medication temporarily before your test.
What Happens During Blood Glucose Tests?
A blood glucose test ordered as part of a blood panel, such as a basic metabolic panel or comprehensive metabolic panel is usually performed at the medical office or clinic. When you arrive at the medical office or clinic, you will be seated in a comfortable chair. Your healthcare provider or a nurse will check your upper arms for an easily accessible vein. This is usually in the inner part of your upper arm on the other side of your elbow. Once they have located a vein, an elastic band is wrapped around your upper arm to make the vein swell with blood. The site of needle insertion at the vein is cleaned with an antiseptic solution. A small needle is then inserted into your vein and the required sample of blood is drawn out. You may feel a slight stinging sensation when the needle goes in and out of your skin. The extracted blood sample is collected in a vial or test tube and preserved for laboratory analysis thereafter. A cotton gauze is applied over the insertion site as the needle is withdrawn to control bleeding. A small bandage is placed over the insertion site after the procedure is complete. The entire process takes around five minutes or less.
However, if you are managing your diabetes at home, you will likely be trained to perform a finger-prick test yourself with the aid of a glucometer and strips. This typically involves the following:
- Wash and dry your hands thoroughly as food and other substances can give you an inaccurate reading.
- Prick your fingertip with the needle (lancet) provided with your test kit
- Touch and hold the edge of the test strip to the drop of blood at your fingertip
- Now, insert the test strip into your glucometer. After a few seconds, the meter will display your blood sugar level on a screen.
Results of Blood Glucose Tests
Normal Blood Glucose Level
A normal (healthy) fasting blood glucose range for an individual without diabetes is 3.9 to 5.5 mmol/L (70 to 99 mg/dL). Values between 2.8 to 3.9 mmol/L (50 and 70 mg/dL) for individuals without diabetes can be considered “normal” too.
Abnormal Blood Glucose Level
If your fasting blood glucose range is 5.6 to 6.9 mmol/L (100 to 125 mg/dL), it generally means you have prediabetes. Individuals with prediabetes have up to a 50 per cent likelihood of developing Type 2 diabetes over the next 5 to 10 years. However, you can take steps to prevent Type 2 diabetes from developing with lifestyle changes.
If your fasting blood glucose range is 7.0 mmol/L (126 mg/dL) or higher on more than one testing occasion, it generally means you have diabetes.
In either of these instances, your physician will likely recommend an HbA1C test before diagnosing you with prediabetes or diabetes. An HbA1c test is a blood test that provides your average blood glucose levels for the last 2 to 3 months.