Fasting Blood Glucose (FBG)
Fasting blood glucose measures the basal concentration of circulating D-glucose following an 8 to 12 hour overnight fast, reflecting hepatic gluconeogenesis and baseline beta-cell insulin secretion.
Standard vs. Optimal Reference Rangesmg/dL
Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.
Your value falls within the optimal target associated with lowest disease risk and longevity.
70 - 99 mg/dL
General reference distribution across unselected commercial populations.
75 - 85 mg/dL
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
In the fasting state, basal insulin suppresses glycogenolysis and phosphoenolpyruvate carboxykinase (PEPCK)-mediated gluconeogenesis in hepatocytes. Hepatic insulin resistance leads to uninhibited glucose output despite normo- or hyperinsulinemia.
Differential Diagnosis
Elevated Levels (FBG High)
- •Type 2 Diabetes Mellitus (>= 126 mg/dL)
- •Impaired Fasting Glucose / Prediabetes (100 - 125 mg/dL)
- •Cushing syndrome / Glucocorticoid excess
- •Acute physiological stress or sympathetic activation
Low Levels (FBG Low)
- •Insulinoma / Exogenous insulin administration
- •Addison disease (adrenal insufficiency)
- •Severe hepatic failure
- •Prolonged therapeutic fasting
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Strict 10 to 12 hour overnight water-only fasting is mandatory for baseline metabolic quantification. Acute psychological stress, acute infectious illness, and sleep deprivation (<6 hours) transiently elevate cortisol and catecholamines, falsely elevating glycemic markers. For glucose and insulin testing, draw blood into sodium fluoride/potassium oxalate tubes or separate serum promptly within 30 minutes to prevent ongoing in vitro red blood cell glycolysis.
Reflexive Testing Protocol:
- Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and HOMA-Beta calculations
- Continuous Glucose Monitoring (CGM) 14-day wear to evaluate glycemic variability and postprandial excursions
- Fasting C-Peptide and high-sensitivity Troponin/hs-CRP to differentiate insulin resistance from beta-cell exhaustion
- Oral Glucose Tolerance Test (OGTT) with simultaneous 0, 30, 60, and 120-minute insulin assays
- Abdominal ultrasound or FibroScan to evaluate hepatic steatosis and non-alcoholic fatty liver disease (MASLD)
Clinical Citations & Primary Literature (1)
- [1]Fasting Blood Glucose and Risk of Cardiovascular Disease in Non-Diabetic Adults - Lancet Diabetes & Endocrinology (2020). PMID: 31926941
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate Fasting Blood Glucose (FBG) into overall healthspan optimization.