What Is Fasting Blood Glucose?
Glucose is a major source of energy for the body’s cells.
Blood glucose levels are regulated by several mechanisms, with insulin, a hormone produced by the pancreas, playing a particularly important role.
The fasting plasma glucose (FPG) test measures the concentration of glucose in the blood plasma after a period of fasting.
It is used to detect abnormalities in glucose metabolism and to diagnose diabetes. [1]
What Are Normal Fasting Blood Glucose Levels?
According to the American Diabetes Association’s (ADA) Standards of Care in Diabetes 2026, the following thresholds apply to non-pregnant individuals:
| Fasting Blood Glucose | Interpretation |
|---|---|
| Below 100 mg/dL | Normal |
| 100–125 mg/dL | Prediabetes |
| ≥126 mg/dL | Diagnostic threshold for diabetes |
These thresholds do not apply in the same way during pregnancy, as different diagnostic criteria are used.
Furthermore, a normal fasting blood glucose result does not necessarily rule out an underlying problem with glucose regulation. [1]
What Does High Fasting Blood Glucose Mean?
Fasting Blood Glucose of 100–125 mg/dL
According to ADA criteria, fasting blood glucose levels within this range indicate prediabetes.
Prediabetes is associated with an increased risk of developing type 2 diabetes.
However, the level of risk varies between individuals and is influenced by several factors. [1]
Fasting Blood Glucose of 126 mg/dL or Higher
A fasting blood glucose level of 126 mg/dL or higher meets the diagnostic threshold for diabetes.
However, in people without clear clinical evidence of hyperglycaemia, the diagnosis must be confirmed by a second abnormal test result.
This may involve repeating the fasting glucose test or using another diagnostic test, such as glycated haemoglobin (HbA1c).
In someone experiencing symptoms of hyperglycaemia, such as frequent urination, excessive thirst and unexplained weight loss, a random plasma glucose level of ≥200 mg/dL can also establish a diagnosis of diabetes. [1]
What Is the Difference Between Fasting Blood Glucose and HbA1c?
Although both tests are used to investigate diabetes, they provide different information.
Fasting blood glucose measures the concentration of glucose in the blood at a specific point in time, following a period of fasting.
By contrast, glycated haemoglobin (HbA1c) provides information about a person’s average blood glucose exposure over approximately the previous two to three months.
Unlike fasting glucose testing, an HbA1c test does not require fasting.
However, certain conditions can affect the reliability of HbA1c results, including some types of anaemia, haemoglobin disorders and conditions that alter the lifespan of red blood cells. [1]
How Is the Test Performed and What Can Affect the Results?
A fasting blood glucose test is usually performed using a standard blood sample.
To ensure an accurate measurement, the following instructions should be followed:
- Fast for at least eight hours before the test.
- Avoid all foods and drinks containing calories.
- Drinking water is allowed.
Blood sampling is generally recommended in the morning after an overnight fast. [2]
Certain factors, including acute infections, severe physical stress and specific medications, can also affect blood glucose levels.
Proper handling of the blood sample by the laboratory is equally important.
Blood cells continue to consume glucose after the sample has been collected. If the sample is not processed appropriately, this can lead to a falsely low glucose result. [2]
Can Type 2 Diabetes Be Prevented if You Have Prediabetes?
For people at increased risk, appropriate lifestyle changes can reduce the likelihood of developing type 2 diabetes.
According to the ADA’s 2026 guidelines, these interventions include:
- Regular physical activity.
- A balanced diet.
- Weight management, when appropriate.
- Personalised support to help maintain lifestyle changes.
The guidelines place particular emphasis on structured diabetes prevention programmes. [3]
Including foods rich in dietary fibre is also important.