Normal Fasting Plasma Glucose Levels
According to current guidelines, normal fasting plasma glucose is defined as less than 100 mg/dL (5.6 mmol/L). 1
Definition of Normal Fasting Plasma Glucose
- Normal fasting plasma glucose (FPG) is defined as less than 100 mg/dL (5.6 mmol/L) according to the American Diabetes Association (ADA) 2003 criteria 1
- This represents a change from earlier criteria that defined normal FPG as less than 110 mg/dL (6.1 mmol/L) 1
- The World Health Organization (WHO) previously defined normal glucose regulation as FPG < 6.1 mmol/L (110 mg/dL) 1
Diagnostic Categories for Glucose Metabolism
- Normal glucose metabolism: FPG < 100 mg/dL (5.6 mmol/L) 1
- Impaired fasting glucose (IFG): FPG 100-125 mg/dL (5.6-6.9 mmol/L) 1
- Diabetes mellitus: FPG ≥ 126 mg/dL (7.0 mmol/L) 1
Risk Stratification Within Normal Range
Even within the normal range, higher fasting glucose levels are associated with increased risk of developing diabetes:
- Each 1 mg/dL increase in FPG within the normal range increases diabetes risk by 6% 2
- Compared to those with FPG < 85 mg/dL, individuals with FPG 95-99 mg/dL have 2.33 times higher risk of developing diabetes 2
- Men with FPG ≥ 87 mg/dL have progressively increased risk of type 2 diabetes compared to those with levels < 81 mg/dL 3
Clinical Implications
- Fasting plasma glucose should be measured after at least 8 hours of no caloric intake 1
- Values should be confirmed by repeat testing on a different day to establish a diagnosis of diabetes or prediabetes 1
- Patients with FPG in the upper range of normal (91-99 mg/dL) who also have other risk factors (elevated triglycerides ≥ 150 mg/dL or BMI ≥ 30) have substantially increased risk of developing diabetes 3
Lower Limit of Normal Range
- While the upper limit of normal FPG is well-established at 100 mg/dL, the lower limit is less clearly defined 4
- Some evidence suggests that FPG < 70 mg/dL may be associated with increased cardiovascular and all-cause mortality 4
- Most clinical guidelines focus on the upper limit rather than establishing a formal lower boundary for normal FPG 1
Practical Considerations
- When interpreting glucose values, it's important to note that plasma glucose values are approximately 11% higher than whole blood glucose values 1
- For screening purposes, fasting plasma glucose is the preferred initial test due to convenience and cost-effectiveness 1
- Patients with normal FPG but risk factors for diabetes may benefit from additional testing with oral glucose tolerance test or HbA1c 1