Interpret Your Fasting Blood Glucose Results
Enter your FBG value below and get an instant, free AI interpretation — a plain-English explanation checked against WHO/IFCC reference ranges.
Medical Disclaimer
This AI-generated interpretation is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Results may vary based on individual health factors not captured here.
Always consult a qualified healthcare professional before making any health decisions. Read full disclaimer →
Fasting Blood Glucose Normal Ranges
Fasting blood glucose (FBG) measures blood sugar after at least 8 hours without food or caloric drink.
| Reference Range | Unit | Notes |
|---|---|---|
| 70 – 99 | mg/dL | Fasting normal |
| 100 – 125 | mg/dL | Prediabetes (impaired fasting glucose) |
Also reported in: mmol/L.Conversion factor: 1 mmol/L = 0.056 mg/dL.
Critical (Panic) Values
Critical Low: < 50 mg/dL. Critical High: > 500 mg/dL. Values outside these limits require immediate clinical attention.
Why Doctors Order the Fasting Blood Glucose Test
FBG above 126 mg/dL on two separate occasions confirms diabetes mellitus. FBG of 100–125 mg/dL indicates impaired fasting glucose (prediabetes), which carries a significant risk of progression to diabetes and cardiovascular disease.
How to Enter Your FBG Result
Fasting Blood Glucose can be reported in mg/dL or mmol/L. Choose the unit printed next to your result on the lab report so it is compared with the matching reference range.
What a Low or High FBG Can Be Associated With
Below the reference range
- Insulin overdose (most common cause of severe hypoglycemia)
- Oral hypoglycemic agents (sulfonylureas — glibenclamide, glipizide)
- Prolonged fasting or starvation
- Insulinoma (insulin-secreting tumor)
- Adrenal insufficiency
Above the reference range
- Type 1 diabetes mellitus (autoimmune, absolute insulin deficiency)
- Type 2 diabetes mellitus (insulin resistance and relative deficiency)
- Gestational diabetes
- Corticosteroid-induced hyperglycemia
- Cushing's syndrome
This interpreter flags a result at or below 50 mg/dL or at or above 500 mg/dL as a critical value. Results that extreme are uncommon — contact your doctor promptly, and seek urgent medical care if you feel unwell.
These are common associations, not a diagnosis. A single result is read alongside your symptoms, history and other tests — discuss it with your doctor.
What Can Change Your FBG Result
Before you read too much into a result, consider whether any of these applied:
- Non-fasting state (most important — eating raises blood glucose)
- Stress, illness, or surgery (causes stress hyperglycemia)
- Medications: corticosteroids (raise), insulin and sulfonylureas (lower)
- Sample processing delay (glucose decreases in unprocessed tubes due to glycolysis)
Preparing for the test: Fast for 8–12 hours before the test. Only water is allowed during fasting.
Symptoms That Often Prompt FBG Testing
- High glucose: excessive thirst (polydipsia), frequent urination (polyuria), blurred vision, fatigue, slow-healing wounds
- Low glucose: trembling, sweating, palpitations, hunger, confusion, loss of consciousness
Want the full clinical guide to Fasting Blood Glucose?
Reference ranges, causes, symptoms, preparation, and FAQs.