Blood Sugar Test or Blood Glucose Test : Purpose, Preparation, Procedure & Normal Range of Results

Blood sugar test or blood glucose test is done to know how well the body is managing blood sugar levels. Usually glucose testing is done to check for pre-diabetes, type 1 diabetes, type 2 diabetes, and gestational diabetes.

Updated: June 16, 2022

Blood sugar test or blood glucose test is done to know how well the body is managing blood sugar levels. Blood sugar tends to raise about an hour after eating, and reduces after that.
If the glucose level doesn't decrease to a normal range even after two hours of eating, that is an indication of insulin resistance or diabetes.
Your body converts the carbohydrates you eat into glucose which is the main source of energy. The amount of glucose in your blood can be measured by a blood glucose test.
Usually glucose testing is done to check for pre-diabetes, type 1 diabetes, type 2 diabetes, and gestational diabetes. Diabetes is a condition that causes your blood glucose level to rise.
The hormone called insulin in our body is responsible for controlling the glucose level. In either case if your body does not produce enough insulin or your body is unable to use the insulin produced, sugar will build up in your blood causing diabetes. Left untreated, increased levels of blood sugar can lead to severe health complications and organ damage.
Blood glucose testing may also be done to test for hypoglycemia, a condition in which the levels of glucose in your blood are too low. This could be due to diabetes medications.
If you are a diabetic you may have to get blood glucose tests done frequently to determine if your condition is being managed well. A high glucose level in a person with diabetes indicates that your diabetes is not being managed properly.


Other possible causes of high blood glucose levels include:

  • prediabetes, which is a condition when you are at increased risk of developing type 2 diabetes
  • kidney problems
  • pancreatitis, or inflammation of your pancreas
  • pancreatic cancer
  • hyperthyroidism, or overactive thyroid
  • stress to the body from illness, trauma, or surgery
  • kidney failure in rare case
  • Cushing's syndrome, a condition when your body produces too much cortisol
  • Low blood glucose levels, or hypoglycemia, may be caused by:
  • insulin overuse
  • starvation
  • hypopituitarism, or underactive pituitary gland
  • insulinoma, which is a type of pancreatic tumor
  • hypothyroidism, or underactive thyroid
  • Addison's disease, where cortisol levels are very low
  • liver disease
  • alcohol abuse

Blood sugar tests are of several types. These include:

  • Fasting blood sugar test
  • Random blood sugar test
  • Glycated hemoglobin (A1C) test
  • Oral glucose tolerance test

Things to be done before a blood glucose test:

Blood glucose tests are either random or fasting tests. For a fasting blood glucose test, you need to fast at least for eight hours before your test. During this period you can not eat or drink anything except water. To avoid fasting during the day time, usually a fasting glucose test is schedule in early morning. As this test provide more accurate results and are easier to make a diagnosis it is very common. In case of random glucose test you can eat and drink before the test.

Medications that can affect your blood glucose levels include:

  • acetaminophen (Tylenol)
  • hormone therapy
  • corticosteroids
  • steroids
  • birth control pills
  • diuretics
  • aspirin (Bufferin)
  • atypical antipsychotics
  • phenytoin
  • epinephrine (Adrenalin)
  • monoamine oxidase inhibitors
  • tricyclic antidepressants
  • lithium
  • sulfonylurea medications

A temporary increase in your blood glucose level can be due to severe stress such as surgery, trauma, stroke or heart attack.

How a blood glucose test is done?

A band will be tied by a technician around your arm so that the veins of the hand are more prominent to prick the injection. The vein is punctured with a fresh, disposable syringe and the blood is withdrawn after the site is cleaned with an alcohol swab. A cotton swab will be given to you after drawing the blood to place on the place where the injection was pricked. You will be asked to apply pressure on the cotton in order to stop the bleeding. You might notice a bruise in the place where the injection was pricked on your skin. This is normal and should fade away in a few days.


Before you undergo this test, you should inform the lab technician if you suffer from a bleeding or clotting disorder or are taking medicines like aspirin, warfarin or other blood-thinning agents, as in such cases the bleeding might take a while to stop.

How can I test myself for diabetes?

You can also use a glucometer to test daily levels of fasting blood sugar or random blood sugar. To do the test using a glucometer you can follow the following steps:

  • Keep ready the testing strip and glucose monitor to receive a blood sample.
  • Cleanse the side of a fingertip with an alcohol swab.
  • Prick the testing area with the niddle provided in the testing kit.
  • Squeeze the testing area around the wound to maximize blood flow, and squeeze a drop of blood onto the test strip.
  • Put the strip into the monitor.
  • Record the blood sugar reading displayed in the monitor.

In most cases, fasting blood sugar is measured immediately after waking in the morning, before you have had anything to eat or drink. It may also be appropriate to test blood sugar before eating or sometimes 2 hours after a meal, when blood sugar has returned to normal levels.

The right time to test depends on treatment goals and other factors. It is not necessary to test between meals unless you are on a diabetes drug that can lower blood sugar. When you are on diabetes drug this test is done to know how well the drug is managing the blood glucose levels. People who are not on medication and if they feel their sugars are low, may test between meals. People with type 1 diabetes also test multiple times a day to check their levels regularly in order to adjust their insulin dosing as they do not make any insulin.

Normal results for blood sugar test:

  • The fasting blood sugar level should be 70-100 mg/dL for people without diabetes and 70-130 mg/dL for people with diabetes.
  • Two hours following a meal the level should be less than 140 mg/dL for people without diabetes and below 180 mg/dL for people with diabetes.


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