Most Accurate Measurement of Blood Glucose
Venous plasma glucose measured by enzymatic laboratory methods (hexokinase or glucose oxidase) is the most accurate method for measuring blood glucose levels. 1
Laboratory Methods vs. Point-of-Care Testing
Laboratory Methods (Gold Standard)
- Enzymatic methods using hexokinase or glucose oxidase are the most standardized and accurate techniques for glucose measurement 1
- Laboratory methods demonstrate minimal imprecision with a coefficient of variation (CV) ≤2.7% at clinically relevant glucose concentrations 1
- These methods are used in virtually all clinical laboratories in the US and provide consistent results across different facilities 1
Point-of-Care Testing Limitations
- Glucose meters (used for self-monitoring or bedside testing) are less accurate than laboratory methods, though significantly better than older visual color-matching techniques 1
- Operator-related errors are more significant than instrument-related errors with glucose meters 1
- Under International Organization for Standardization standards, glucose meters should have >95% of readings within ±15 mg/dL for glucose <75 mg/dL and within 20% for higher values 1
- Many meters fail to meet these standards in real-world clinical settings, particularly in critically ill patients 1
Sample Collection and Processing Considerations
Sample Type
- Plasma is recommended over whole blood for diagnostic purposes 1
- Glucose concentrations in plasma are approximately 11% higher than in whole blood with normal hematocrit due to higher water content in plasma 1
- Most modern glucose meters are calibrated to provide plasma-equivalent readings 1
Sample Handling
- Glycolysis occurs rapidly in whole blood samples (5-7% decrease in glucose per hour) if not properly processed 1
- To minimize glycolysis, blood should be collected in tubes containing citrate buffer, sodium fluoride, and EDTA, or immediately placed in an ice-water slurry and plasma separated within 30 minutes 1
- Acidification of blood with citrate buffer is particularly effective at inhibiting glycolysis, with only 0.3% decrease in glucose at 2 hours and 1.2% at 24 hours 1
Special Considerations for Different Clinical Settings
Critical Care Settings
- For critically ill patients, arterial or venous whole blood sampling is preferred over capillary (fingerstick) testing, especially for patients in shock, on vasopressors, or with peripheral edema 1
- Plasma glucose values from arterial blood are approximately 0.2 mmol/L higher than peripheral venous blood 1
- Several factors can affect glucose meter accuracy in ICU settings, including anemia, hypoxia, and certain medications 1
Diabetes Management
- While continuous glucose monitoring (CGM) provides valuable trend data and can detect glycemic variability, it measures interstitial fluid glucose rather than blood glucose and has a physiological lag time 2
- For diagnostic purposes and calibration of other methods, laboratory plasma glucose remains the reference standard 1
Common Pitfalls and How to Avoid Them
- Low hematocrit can falsely elevate glucose meter readings due to lower erythrocyte mass 1
- Improper storage of test strips (exposure to humidity or excessive temperature) can falsely elevate results 1
- Certain drugs like ascorbic acid, acetaminophen, dopamine, and mannitol can interfere with some glucose meter readings 1
- Glucose meters are less reliable in the hypoglycemic and hyperglycemic ranges 1
- To ensure accuracy, regular calibration of meters and proper training of users is essential 1
Accuracy Goals for Glucose Measurement
- For plasma glucose, a CV ≤2.2% has been suggested as a target for imprecision, with 0% bias 1
- The goal for glucose analysis should be to minimize total analytical error and methods should be without measurable bias 1
- When compared with reference measurement procedures, significant bias (up to 13%) has been observed in some laboratory methods, which could lead to misclassification of individuals near diagnostic thresholds 1