Fasting Glucose Test Fact Sheet

Diabetes and its precursor, pre-diabetes, cause few symptoms, particularly early on in the progression of the condition. Blood sugar or blood glucose testing is common for screening apparently healthy people to determine whether they have diabetes or are at risk of diabetes. Public health fairs and routine examinations frequently include blood glucose tests. One of these tests is known as a fasting glucose test, though this test is more likely to performed at a prearranged appointment because it requires overnight fasting beforehand. People who are overweight or who have a family history of diabetes are likely to benefit from this screening test, as are adults age 40 and older. As people age, their bodies ability to regulate blood glucose can decline, making the fasting glucose test beneficial for older adults.

When people eat carbohydrates, the body breaks down the carbs into glucose. With the assistance of insulin, the body uses glucose for energy. Without insulin, glucose cannot enter cells; instead, it remains in the blood, causing high blood sugar levels. The inability to produce insulin or an impaired ability to make or use it defines diabetes. A high level of fasting glucose suggests diabetes, especially if high levels are found more than once.

Overview of the test

A fasting glucose test or FBS, is a simple blood test that looks at how much sugar is in a blood sample. This test screens for abnormal blood glucose ranges, either too much or too little. Doctors may use it to screen for diabetes.

Results could indicate a person has diabetes or is in a blood glucose range that indicates pre-diabetes, which is when glucose levels are moderately elevated. People with pre-diabetes do not have symptoms.

How is it done

A fasting glucose test is simple, but people must follow certain rules to get accurate results. People must avoid food and drink for at least eight hours prior to getting their blood drawn for testing. Ideally, patients will fast overnight and then get the test in the morning before breakfast. Engaging in physical activity can affect the results, so even if someone fasts during the day and then has the test the score may not be accurate.

A normal fasting blood glucose range is between 70 and 99 milligrams per deciliter. A score of 100 to 125 milligrams per deciliter indicates pre-diabetes, also called impaired fasting glucose. Results above 126 milligrams per deciliter suggests diabetes.

Who Does it?

Health care professionals generally perform this test, especially for screening purposes. People can perform the test on themselves with a finger prick.

When and How Often?

Doctors may use the fasting blood glucose test on patients who have signs of diabetes. Some signs could include elevated thirst, blurry vision, fatigue, or infections that heal at a decreased rate. These are all symptoms of too much blood sugar.

Doctors can also order the test for patients with signs of low blood sugar, such as perspiration, anxiety, shaking, impaired vision, hunger, and mental confusion. People who experience their first seizure, behavioral changes or fainting may need a fasting glucose test as well.


The cost of a fasting blood glucose test is usually covered by insurance. The test is frequently done as part of a routine physical and charged as part of the package. The out of pocket price for a fasting glucose test is only around $5 to $40, but that does not include the doctor’s visit.


It is crucial that people fast completely before a fasting glucose test. Any food could dramatically affect results. Major stress can also cause a rise in blood sugar. A trauma, surgery or significant health problem can temporarily cause a spike in blood glucose that will change results, and some medications will affect blood glucose levels.


Last reviewed 26/Feb/2014


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Whilst wielding a couple of dumbbells in a gym class in 2003, Kate experienced an epiphany around the lack of accepted best practice guidelines when it came to staying well and avoiding disease. Kate realized that she had no chance of slowing her own aging process unless she became better educated about her options.

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