Normal Fasting Blood Glucose Levels
Normal fasting blood glucose is defined as less than 100 mg/dL (5.6 mmol/L) according to the American Diabetes Association guidelines. 1
Diagnostic Categories for Glucose Metabolism
- Normal fasting plasma glucose: <100 mg/dL (5.6 mmol/L) 2, 1
- Impaired fasting glucose (prediabetes): 100-125 mg/dL (5.6-6.9 mmol/L) 2
- Diabetes mellitus: ≥126 mg/dL (7.0 mmol/L) 2
Clinical Significance of Fasting Glucose Levels
- Even within the normal range, higher fasting glucose levels (87-99 mg/dL) are associated with increased risk of developing type 2 diabetes compared to lower normal values (<81 mg/dL) 3
- Individuals with fasting glucose in the high normal range (95-99 mg/dL) have a 1.53 times higher risk of cardiovascular disease compared to those with levels <80 mg/dL 4
- The risk of developing diabetes increases progressively as fasting glucose levels rise, even within the normoglycemic range 5
Proper Measurement of Fasting Blood Glucose
- Fasting blood glucose should be measured after at least 8 hours of no caloric intake 1
- For diagnostic purposes, abnormal values should be confirmed by repeat testing on a different day 1
- Plasma glucose values are approximately 11% higher than whole blood glucose values, which is important to consider when interpreting results 1
Risk Assessment and Screening
- Individuals with risk factors for diabetes should undergo regular screening with fasting plasma glucose tests 2, 1
- Risk factors include: family history of diabetes, BMI >25 kg/m², sedentary lifestyle, hypertension, dyslipidemia, history of gestational diabetes, and certain ethnic backgrounds (Black, Latin American, Native American, Asian-Pacific Islander) 6
- Combining fasting glucose levels with other risk factors (such as triglyceride levels ≥150 mg/dL or BMI ≥30) significantly increases the predictive value for future diabetes development 3
Preventive Interventions for Those with Prediabetes
- For individuals with prediabetes (fasting glucose 100-125 mg/dL), lifestyle modifications including 5-7% weight loss and at least 150 minutes of physical activity per week are recommended 6, 7
- Metformin may be considered for those at highest risk, particularly individuals <60 years with BMI ≥35, fasting glucose ≥110 mg/dL, or HbA1c ≥6.0% 7
Important Caveats
- The World Health Organization previously defined normal glucose regulation as FPG <110 mg/dL, which differs from the current ADA criteria of <100 mg/dL 1
- When using different diagnostic tests (fasting glucose, oral glucose tolerance test, or HbA1c), results may sometimes be discordant; in such cases, the test whose result is above the diagnostic cut point should be repeated for confirmation 2
- Fasting plasma glucose is generally preferred as the initial screening test due to convenience and cost-effectiveness, but patients with normal FPG and risk factors may benefit from additional testing with oral glucose tolerance test or HbA1c 1