Normal Laboratory Values
Normal fasting blood glucose is less than 100 mg/dL (5.55 mmol/L), blood lactate is less than 2.3 mmol/L, and serum unbound free fatty acids average 7.5 nM (with total FFA approximately 434 μEq/L in healthy individuals).
Blood Glucose
The 2023 American Diabetes Association guidelines establish that normal fasting plasma glucose (FPG) is less than 100 mg/dL (5.55 mmol/L) 1. However, this represents a clinical threshold rather than an absolute physiologic boundary.
Key nuances about glucose interpretation:
- In healthy individuals, mean FPG is approximately 4.6-4.9 mmol/L (83-88 mg/dL) with biological variation showing within-person coefficient of variation (CV) of 4.7-5.7% 1
- The 95% confidence interval for a true glucose of 7.0 mmol/L (126 mg/dL) spans 6.1-7.9 mmol/L (110-142 mg/dL) when accounting for biological variability 1
- Even within the "normal" range, higher FPG levels carry increased diabetes risk: men with FPG 87-99 mg/dL have progressively increased risk of developing type 2 diabetes compared to those with FPG <81 mg/dL 2
Clinical pitfall: Don't assume values below 100 mg/dL are uniformly "safe"—the upper end of normal (91-99 mg/dL) combined with obesity (BMI ≥30) or elevated triglycerides (≥150 mg/dL) increases diabetes risk 8-fold 2.
Blood Lactate
Normal lactate is less than 2.3 mmol/L 3. This threshold has important prognostic implications even within the "normal" range.
Critical interpretation points:
- Lactate levels of 1.4-2.3 mmol/L (still technically "normal") are associated with significantly increased mortality and organ dysfunction in septic shock patients compared to lactate ≤1.4 mmol/L 3
- Lactate ≤1.4 mmol/L predicts beneficial response to vasopressin in septic shock 3
- In healthy individuals during 24-hour monitoring, lactate levels vary but remain consistently below 2.3 mmol/L 4
Clinical caveat: The traditional upper limit of 2.3 mmol/L should not be interpreted as a binary cutoff—values in the 1.4-2.3 mmol/L range warrant clinical attention in critically ill patients.
Serum Free Fatty Acids (FFA)
Normal unbound FFA averages 7.5 ± 2.5 nM, while total FFA in healthy individuals averages 434 ± 45 μEq/L 5, 6.
Important distinctions:
- Unbound (free) FFA: 7.5 nM mean, with standard deviation of 2.5 nM 5
- Total FFA: Approximately 434 μEq/L in normal-weight healthy individuals 6
- FFA levels show minimal variation with gender and age but increase modestly (1.5 nM) after overnight fasting 5
Pathologic elevations:
- In type 2 diabetes, total FFA levels rise to 672 ± 35 μEq/L (approximately 50% higher than normal) 6
- Newly diagnosed diabetic patients show three-fold elevation in plasma FFA compared to controls 7
- FFA levels are particularly elevated overnight (midnight to 0800) in severe diabetes 4
Clinical significance: Elevated FFA levels increase basal hepatic glucose production and induce hepatic insulin resistance, providing a mechanistic link between obesity and diabetes development 8. FFA measurements combined with protein glycation markers provide diagnostic accuracy of 87-91% for type 2 diabetes 7.