Blood Sugar (Glucose) Fasting (FBS) Lab Test

Urine sugar
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Clinical Definition of Blood Sugar (Glucose) Fasting (FBS)

Blood sugar (glucose) is usually present in the urine at very low levels or not at all. Abnormally high amounts of sugar in the urine, known as glycosuria, are usually the result of high blood sugar levels. High blood sugar usually occurs in diabetes, especially when untreated. It serves as the main source of energy used by the body. Insulin is a hormone that helps the body's cells to use the glucose. Excess or shortage of insulin in the body causes an imbalance of the blood glucose in the body, leading to its severe drop or drastic increase in the blood. Blood glucose levels that remain high over time can cause damage to the eyes, kidneys, nerves and blood vessels. Chronic low glucose levels can lead to brain and nerve damage.

Fasting blood sugar is a test for glucose content in a person’s blood that, as the name suggests, is conducted after fasting. The test is generally carried out in the morning, after an overnight fasting. As a part of the test, a sample of the patient’s blood is collected and then sent to the lab for testing.

A fasting blood sugar test offers information about how the body is managing the blood sugar levels. Normally, the range of glucose in a person’s blood is between 70 to 100 mg/dl. Fasting blood sugar levels between 100 to 126 mg/dl are considered as pre-diabetic or impaired fasting glucose and blood sugar levels of 126 mg/dl or higher are diagnosed as diabetes.

When do you expect results?

24 to 36 Hours

Why Get Tested?

This test determines the quantity of glucose present in the blood.

It is a test generally called for during routine health checkups to analyse the recomended glucose level.

To monitor and detect treatment of diabetes that occurs during pregnancy (gestational diabetes), monitor glucose levels in persons with diabetes, Hyperglycemia, hypoglycemia, Diabetes,Pre-diabetes and Urine glucose analysis is usually done as part of a routine urinalysis.

A Fasting Blood Sugar Test is prescribed to patients who are either suffering from diabetes or are at a risk of suffering from it. Although any major changes in the pattern of the blood sugar demand a thorough checkup by the doctor, there are a few symptoms which indicate that you need to consult a doctor sooner rather than later. These are: –

When your blood sugar suddenly becomes uncontrolled

You come across new symptoms of diabetes

Old diabetes conditions keep getting worse

Unusual rise or fall in blood sugar levels

You experience very high blood pressure levels

You have started or stopped taking a medication

When an infection or sore is not healing

Diabetes can be kept under control through proper monitoring and care.

What does the test detect?

This test is primarily carried out to check for the presence of diabetes in the patients. Normally, the amount of sugar in one’s blood is controlled by a hormone, known as insulin. However, in case of diabetes, the body fails to produce enough insulin required to carry out the process smoothly. This results in the rise in sugar levels in the blood of the individual concerned.


Reason to take Blood Sugar (Glucose) Fasting (FBS) Test

Symptoms associated with hyperglycemia are: 

Increased thirst

Increased urination (especially at night)



Extreme tiredness

Blurred vision

Slow-healing infections

Erection problems

Irregular menstrual cycles

Tingling sensation or numbness in the hands and feet 

Unexplained increase in appetite

Unexplained weight gain or weight loss

Irregular menstrual cycles

Symptoms associated with hypoglycemia

Hunger, Anxiety, Confusion Sweating, Trembling and Blurred vision.

Preparations Needed for Blood Sugar (Glucose) Fasting (FBS) Test

"Fasting Required.
Fasting samples have to be collected after a minimum 8-hour overnight fasting status.
Clear fluids like water is allowed during this period. Refrain from consumption of early morning beverages like tea, coffee and milk until specimen collection is completed.
In case of diabetics on oral or injectable hypoglycemic agents, consult your physician about continuing with these medications prior to specimen collection.
For a 2-hour postprandial test, the meal must be eaten exactly 2 hours before the blood sample is taken.
No special preparation is required before having a random blood sugar test."

To prepare for a fasting test, you may be asked to refrain from eating or drinking anything, except water, for at least eight hours prior to the test. To make it more convenient, try scheduling this test with your doctor first thing in the morning.

Some medications tend to affect the blood glucose level, which is why it is vital that you mention any medicines that you are taking to your doctor. This should include all herbal supplements, and prescription and over-the-counter drugs as well. You may be asked to temporarily stop the consumption of a few or all of them, before the test.


Sample Required?

"Specimen type:
Serum / Plasma (Blood Sample),Specimen collection procedure:
Venipuncture - (Collection of blood from a vein, usually from the arm)."

How do you understand this result?

Reference RangeInterpretation
70-110Normal Glucose Tolerance
110-126Impaired Glucose
>126Provisional Diag. Diabetes Mellitus
AbsentUrine Sugar

A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges.