Fasting Blood Sugar Test
General, Tests & Procedures

Fasting Blood Sugar Test – Prep, Procedure, Results Interpretation

Fasting blood sugar test is a test used to determine the amount of sugar present in a blood sample after a person has fasted overnight. Fasting really means refraining from eating or drinking any food or liquids other than water for at least 8 hours. The fasting blood glucose (sugar) test is used to detect diabetes.

Usually, a blood sample is taken in a lab or a hospital, in the morning before the person has his breakfast. The normal range for fasting blood glucose is between 70 to 100 mg/dl. Fasting glucose levels between 100 and 126 mg/dl indicate pre-diabetes, and the person is declared diabetic if the fasting blood glucose levels are 126mg/dl or higher.

How the Blood Sugar Levels Vary With Meals?

How the Blood Sugar Levels Vary With Meals?
Blood Sugar Test

Blood sugar levels rise following a meal and usually peak about one hour after eating. The rise in the blood sugar and the precise timing of its peaking depends on the food a person has eaten. Large meals often cause blood sugar levels to rise, and so do meals containing high-sugar carbohydrates such as white bread and sweet snacks.
Normally, a rise in the blood sugar prompts the pancreas to release insulin, and the insulin lowers the blood sugar by breaking it down so that the body can use it for energy or store it for later use. However, people with diabetes may face the following problems:

  • Patients with Type 1 Diabetes do not produce the right amount of insulin required because the body attacks the cells that produce insulin
  • Patients with Type 2 Diabetes do not respond well to the insulin produced by the body, and later, may fail to produce enough insulin.

In both cases, the fasting blood sugar test shows elevated blood sugar levels.

Therefore, Fasting Blood Sugar Depends on 3 Factors:

  • The contents of the last meal, i.e., dinner
  • The size of the last meal
  • The body’s ability to produce insulin and its ability to respond to the insulin it produces

Fasting Blood Sugar Test: Preparation and Procedure

Fasting blood sugar test is done normally to measure the blood glucose level after a certain time of fasting. In healthy people, the insulin hormone helps reduce blood sugar levels after fasting, but the hormone does not function properly in diabetics, so the glucose levels are found to be higher. The test is done to diagnose diabetes or to check the effectiveness of diabetes drugs in persons already diagnosed with diabetes.

The best time to get a fasting blood glucose test done is in the morning, and the test is done after a person has fasted for at least 8 hours. And, before getting the test done, it is important to inform your doctor about the medicines you take regularly, including prescription drugs and over-the-counter drugs. Your doctor may advise you to stop taking a particular medicine or to change the dosage temporarily before the test.

A Tube of Blood is Needed for Conducting the Fasting Blood Glucose Test, and so, The Lab Technician will Draw the Blood as Follows:

  • He will wrap an elastic band around your upper arm
  • Clean the skin over the area from where the blood is drawn with an antiseptic, i.e., either the inside of your elbow or the back of your hand
  • Insert a needle in a suitable vein
  • Place a tube at the puncture site and collect blood
  • Remove the needle and elastic band once the blood is drawn, and put a bandage over the puncture site.

The whole process will take about 1 to 2 minutes.

[ReadBlood Tests That Require Fasting]

Interpreting The Fasting Blood Sugar Test Results

Fasting Blood Sugar Test Results

As mentioned earlier, a person is considered to have a normal reading if his fasting blood sugar level ranges from 70 to 100 mg/dl. A fasting blood glucose level in the range of 100 to 126 mg/dl indicates prediabetes, and a person with a reading higher than 126 mg/dl is considered diabetic.

Symptoms of Unhealthy Fasting Blood Sugar

If your Fasting Blood Sugar is Very Low, You May Face the Following Symptoms:

  • Shakiness and Excessive Sweating
  • Weakness
  • Drowsiness and tiredness
  • Increased rate of heartbeat
  • Lack of concentration and coordination
  • Paleness of skin

Abnormally High Blood Sugar Levels will Cause the Following Symptoms:

  • Increased thirst or hunger
  • Increased frequency of urination
  • Blurred vision
  • Headache
  • Fatigue

Both, very high and very low blood sugar levels may cause loss of consciousness and seizures if left untreated for a long time.

How to Maintain Healthy Fasting Blood Sugar Levels?

It is Important to Follow A Healthy Diet to Keep Fasting Blood Sugar Levels from Rising High. Some Tips Include:

  • Lowering sodium intake
  • Reducing or completely avoiding sweetened snacks
  • Choosing whole-grain bread and pasta over low-nutrient and high-calorie white bread and pasta
  • Eating fiber-rich foods which help lower the blood glucose
  • Eating high-protein foods which help keep you feeling fuller and avoid mid-meal snacking

People on diabetic medication who are prone to experience sudden dips in blood sugar should follow a similar diet, and also take proactive steps to prevent such incidences. These include:

  • Having regular meals
  • Increasing food intake and having frequent snacks during higher than normal physical activity
  • Limiting or completely avoiding alcohol
  • Consulting a physician in case of vomiting or diarrhoea

Thus, a fasting blood sugar test done at regular intervals will help the patients and the doctors with a deeper understanding of the patient’s diabetes status and how the medications prescribed for the condition are helping the patient. Diabetes requires constant monitoring and the treatment may be needed to be changed over time. Diabetics can help themselves by maintaining a detailed health log and staying committed to the dietary and lifestyle changes prescribed by the doctor.

Medically Reviewed By
Dr. Kaushal M. Bhavsar (MBBS, MD)Assistant Professor in Pulmonary Medicine, GMERS Medical College, Ahmedabad