Fasting blood glucose (FBS) measures the sugar in your blood after at least 8 hours without food.
- Normal range (adults)
- 70–99 mg/dL (3.9–5.5 mmol/L)
- Sample
- Blood
- Fasting
- Yes — 8 to 10 hours without food. Water is allowed.
- Also called
- FBS, Fasting Blood Sugar, Fasting Blood Glucose, Glucose Fasting, FBG, Blood Glucose Fasting, Fasting Plasma Glucose, FPG
Fasting Blood Glucose normal range
| Group | mg/dLConventional units: US, South Asia | mmol/LSI units: UK, Europe, Australia, international |
|---|---|---|
| Adults | 70–99 | 3.9–5.5 |
100–125 mg/dL (5.6–6.9 mmol/L) is prediabetes; 126 mg/dL (7.0 mmol/L) or above on two tests is diabetes.
Your report may use either unit system; labs in the Gulf often print both. Ranges also vary slightly between laboratories, so the range printed on your own report is the one to go by.
Why is the Fasting Blood Glucose test done?
It is the standard screening test for diabetes and prediabetes, and is used to monitor treatment.
What does a high Fasting Blood Glucose level mean?
100 to 125 mg/dL (5.6 to 6.9 mmol/L) is prediabetes; 126 mg/dL (7.0 mmol/L) or above on two occasions means diabetes. Over years, high sugar damages blood vessels, eyes, kidneys and nerves.
Common causes
- Type 2 diabetes or prediabetes
- Overweight and inactivity
- Not fasting properly before the test
- Stress, illness or steroid medicines
- Type 1 diabetes, pancreatitis or hormonal conditions (less common)
Diet and lifestyle tips
- Cut sugar, sweets, sweet tea and soft drinks
- Swap white rice and white bread for smaller portions of whole grains, brown rice or chapati made with whole-wheat flour
- Fill half your plate with vegetables; add protein (eggs, fish, chicken, lentils) to every meal
- Choose whole fruit over juice and limit dates and mangoes to small portions
- Walk for 10 to 15 minutes after meals
- Lose 5 to 10% of body weight if overweight
What does a low Fasting Blood Glucose level mean?
Low glucose (hypoglycemia), below about 70 mg/dL (3.9 mmol/L), causes shaking, sweating, hunger, confusion and can lead to fainting.
Common causes
- Diabetes medicines (insulin or sulfonylureas) with missed meals
- Long fasting or heavy exercise
- Alcohol
- Rare hormonal or liver conditions
Diet and lifestyle tips
- If symptoms occur: take 15 g of fast sugar (half a glass of juice or 3 to 4 glucose tablets), then recheck after 15 minutes
- Do not skip meals if you take diabetes medicine
- Include protein and fibre at each meal to keep sugar steady
When should you see a doctor?
See a doctor if your fasting glucose is 100 mg/dL (5.6 mmol/L) or above. Seek urgent care for very high sugar with vomiting or drowsiness, or for low sugar with confusion.
Last updated
This page is for general education and is not a diagnosis. Normal ranges differ between laboratories, so always compare your result with the reference range printed on your own report, and discuss abnormal results with your doctor.