Fasting Blood Sugar
- Sample Type
- Plasma
- Fasting
- Required
- Unit
- mg/dL
Function
The Fasting Blood Sugar (FBS) test measures the amount of glucose in the blood after an overnight fast. Glucose is the primary source of energy for the body's cells, regulated primarily by the hormones insulin (which lowers blood sugar) and glucagon (which raises it).
Why it is Ordered
This is a foundational screening tool for Diabetes Mellitus and Prediabetes. It is ordered during routine physicals or when a patient presents with symptoms of hyperglycemia, such as excessive thirst (polydipsia), frequent urination (polyuria), or unexplained weight loss.
Associated Conditions
- Type 2 Diabetes: Consistently high levels indicate insulin resistance or insufficient insulin production.
- Prediabetes: Levels between 100-125 mg/dL suggest a high risk for developing full-blown diabetes.
- Insulinoma: A rare pancreatic tumor that can cause dangerously low blood sugar.
- Metabolic Syndrome: FBS is a key diagnostic criterion for this cluster of conditions that increase heart disease risk.
Clinical Importance
Maintaining glucose within a narrow range is vital for organ health, particularly the brain and kidneys. Chronic hyperglycemia leads to microvascular damage, affecting the eyes, nerves, and cardiovascular system. Conversely, severe hypoglycemia can lead to loss of consciousness and is an acute medical emergency.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Fasting blood sugar is extremely sensitive to the duration of the fast; consuming anything other than water within 8-12 hours of the test will invalidate the result. Additionally, 'white coat syndrome' or acute stress can cause a cortisol spike, which transiently raises glucose levels. Certain medications like corticosteroids or diuretics are also known to elevate blood sugar levels independently of diabetic status.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Fasting Blood Sugar:
Official Sources
Research & Guidelines
- PubMed: Fasting Blood Sugar Clinical GuidelinesNCBI / PubMed
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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