FBS Test: How Much Sugar Circulates In Your Body?

FBS Test

Elevated blood sugar level is a lifestyle-related condition whose incidence is increasing at an alarming rate. In events of suspecting this abnormality, physicians immediately order an FBS Test (fasting blood sugar) for confirmation.

Increased sugar level in the blood is a result of a defect in our endocrine system, specifically the pancreas. The pancreas is responsible for making the hormone insulin, which removes sugar from the blood and transfers them inside the cells.

If a dysfunction arises in the pancreas, an increase of glucose in the blood may occur.

Therefore an early acquisition of FBS results is essential for immediate treatment of elevated blood sugar levels. This helps to prevent a further elevation of glucose in the blood and stops the development of diabetes complications.

What is an FBS Test?

An FBS test, also commonly known as FBG test (Fasting Blood Glucose), is a frequently ordered blood chemistry for monitoring the amount of sugar in the blood. Physicians usually request it when they see signs of diabetes in their patients.

As the name suggests, an FBS test is only done when a patient fasts to a certain degree, otherwise the results will show false positives.

A false-positive result for an FBS means that there will be a lot of sugar found in the blood. However, the result is not conclusive since the patient did not follow the proper steps before the test is done.

What Do the Values Found in an FBS Test Indicate?

When looking at a fasting blood sugar test, there are 3 categories for the interpretation of the acquired test results. These categories are identified on the basis of the concentration of sugar per volume of blood.

Normal FBS Test Result

An FBS test result below 100 mg/dl is considered normal. This means that the sugar circulating in your blood is within the safe range. There are no negative connotations for this result.

Elevated FBS Test Result

If the FBS result is 100 mg/dl to 125 mg/dl, the patient is considered to be in the prediabetes stage. Although not yet diabetic, this result indicates that the sugar in the patient’s blood is already elevated. The patient may also be at high risk for developing diabetes.

High FBS Test Result

An FBS result of 126 mg/dl or higher means that the patient is already diabetic. The patient will then be subjected to medications to prevent further elevation. And He/She should undergo lifestyle modifications as well as follow a proper diet regimen.


What is an FBS Test Used For?

Identifying Risk for Diabetes

An FBS test result can identify people who are at risk for diabetes and people who already have diabetes. By comparing the patient’s results with the set standards, the physician will be able to identify where the patient’s FBS level falls.


Test Effectivity of Medications

An FBS test may be routinely requested when a patient is in a continuous medication. The results could tell the physician whether the glucose suppressant is working or not. Monitoring the drug’s effectivity is important in managing a diabetic patient’s condition.

What is the Principle Behind Fasting Blood Sugar Test?

The mechanism of a fasting blood sugar test can be explained through the action of the hormones produced by the pancreas: insulin and glucagon.

FBS Test Diabetes and Insulin Insulin

Insulin is a hormone that allows the body to sequester sugar away from the circulation. They function by letting glucose enter the cells of our body where they can be further metabolized or stored.

The resulting phenomenon will be a decreased sugar in the circulation and increased sugar intracellularly.


Glucagon, on the other hand, is the counterpart of insulin.

When the body senses that there is not enough sugar in the bloodstream, the brain signals the pancreas. This signalling pathway leads into the release of glucagon from pancreatic cells into the circulation.

Glucagon then acts on cells to release the stored sugar into the bloodstream. Thus, resulting in an increased sugar in the circulation and decreased sugar inside cells.

Hormonal Action in the Fasting State

When the body is on a state of fasting, the source of nutrients, as well as glucose, is cut-off. Therefore there will be a decrease in blood sugar level since the supply is gone.

A decrease in blood sugar level results in the release of glucagon, which mobilizes stored glucose into the bloodstream.

The increase in blood sugar concentration, due to the action of glucagon, will then result in the release of insulin.

The released Insulin will then act on excess sugar and carry them back inside the cells. This physiologic response attempts to counter the over-increase of glucose in the circulation.

How Does It Reflect in the FBS Test Result?

If the patient is normal, the FBS test should show a sugar level below 100 mg/dl. This means that the body is capable of secreting enough insulin to respond to the increase in blood sugar concentration.

However, if the FBS test result shows a higher blood sugar level compared to the standards, this may mean that the body is not capable of producing enough insulin (Diabetes Type 1). Or the body is not reacting properly to insulin (Diabetes Type 2).

What To Do Before Taking an FBS Test


An FBS Test will not be an accurate FBS test without fasting. Before taking the test you should not eat anything, aside from drinking water for 8-14 hours. Check our Patient Preparation Guide.

It may be in your best interest to schedule an FBS test in the morning to avoid having to fast for a long period.

Inform Your Physician


Before doing an FBS test you should inform your physician of any medications that you are currently taking. Some drugs have side effects that increase the concentration of sugar in the blood. This may impede proper diagnosis if left unnoticed.


Some examples of medications that may cause increased blood sugar levels are:

– Corticosteroids

– Birth Control Pills

– Aspirin

– Epinephrine

– Phenytoin


Stress and Trauma

Aside from medications, some stresses also cause an increase in blood sugar concentration. Inform your doctor regarding recent surgeries, heart attack, trauma, stroke, and anything of the likes.


Conclusion: So Why Do You Need to Fast for an FBS Test?

Fasting gets rid of the food factor which may affect the results when not disqualified. When fasting, the acquired results will be purely about your own body solving the issues on its own. This way, the interpretation will be more accurate and on point.

If your patient cannot make the trip to the lab, LCM Diagnostics has a Home Service option. Contact us today.

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