Glucose (Fasting)

High blood glucose levels (hyperglycemia) may be a sign of prediabetes or diabetes. Prediabetes is a condition in which your blood glucose levels are higher than what is healthy for you, but not high enough to be considered diabetes. If you have diabetes, your body can't make insulin or can't use it as well as it should, or both. Too much glucose stays in your blood and doesn't reach your cells. This can cause glucose levels to get too high. If blood glucose isn't controlled, it can lead to serious, long-term health conditions, such as heart disease and nerve problems.

High blood glucose may also be caused by other conditions that can affect insulin or glucose levels in your blood, such as problems with your pancreas or adrenal glands, and side effects from certain medicines. Glucose testing also helps in evaluating less common carbohydrate metabolism disorders, including unexplained low blood sugar and pancreatic islet cell tumors.

Low blood glucose levels (hypoglycemia) are often caused by certain diabetes medicines for type 1 diabetes or type 2 diabetes, including insulin. In people without diabetes, low blood glucose is much less common. It may be caused by certain medicines and conditions, such as some kidney or liver diseases. Without treatment, severe low blood glucose can lead to major health problems, including seizures and brain damage.

The meaning of your test results will depend on which test you had, the results of other tests, and your medical history. Ask your provider what your test results say about your health.

For a fasting blood glucose test (typically after at least 8 hours without food), the American Diabetes Association uses these ranges: less than 100 mg/dL is normal; 100 to 125 mg/dL is called prediabetes (also known as impaired fasting glucose); and 126 mg/dL or higher on more than one test usually indicates diabetes. Your provider may also use other tests, such as A1C or an oral glucose tolerance test, to confirm a diagnosis.

In general, if your results show higher than normal glucose levels, it may mean you have or are at risk for getting diabetes. Prediabetes and diabetes are the most common causes of high glucose levels, though other conditions can contribute as well.

If you have diabetes, glucose levels that are lower than normal for you may be related to your diabetes medicines or other factors. Talk with your provider to understand what your results mean for you.