What is the normal range for fingerstick blood sugar (BS) measurements?

Normal Range for Fingerstick Blood Sugar Measurements

The normal range for fingerstick blood sugar (BS) is 90-150 mg/dL (5.0-8.3 mmol/L) for fasting measurements and 90-180 mg/dL (5.0-10.0 mmol/L) for non-fasting or postprandial measurements. 1

Understanding Fingerstick Blood Sugar Ranges

Target Ranges by Clinical Context

• Fasting glucose target: 90-150 mg/dL (5.0-8.3 mmol/L) 1
• Pre-meal glucose target: 90-150 mg/dL (5.0-8.3 mmol/L) 1
• Post-meal glucose target: Generally up to 180 mg/dL (10.0 mmol/L) 1
• Hospitalized patients: 140-180 mg/dL (7.8-10.0 mmol/L) 1, 2

Special Populations

• Older adults: Target ranges may be adjusted based on health status and goals of care 1
  • Healthy older adults: Similar targets as general population
  • Frail older adults or those with limited life expectancy: Less stringent targets may be appropriate
• Critically ill patients: 140-180 mg/dL (7.8-10.0 mmol/L) 1, 2
• Terminally ill patients: Higher targets up to 250 mg/dL may be acceptable 1, 2

Important Considerations for Fingerstick Blood Sugar Testing

Accuracy Factors

• Fingerstick measurements may differ from laboratory plasma glucose values by up to 15-20% 1
• Factors affecting accuracy include:
  • Poor peripheral circulation 1, 3
  • Raynaud's phenomenon 3
  • Peripheral edema 1
  • Shock or vasopressor use 1
  • Extreme hematocrit values 1

Testing Site Considerations

• Arterial or venous samples are more accurate than fingerstick capillary blood in patients with:
  • Hypotension 1
  • Peripheral edema 1
  • Vasopressor therapy 1
  • Poor peripheral circulation 1, 3

Timing Considerations

• Fingerstick measurements taken 1 hour after meals may show significant differences compared to venous samples (average bias of -6.02 mg/dL) 4
• Pre-meal and 2-hour post-meal fingerstick measurements show better correlation with venous samples 4

Hypoglycemia and Hyperglycemia Thresholds

Hypoglycemia Levels

• Hypoglycemia alert value: ≤70 mg/dL (3.9 mmol/L) 2
• Clinically significant hypoglycemia: <54 mg/dL (3.0 mmol/L) 2
• Severe hypoglycemia: Any level associated with severe cognitive impairment requiring assistance 2
• Fasting glucose <100 mg/dL may predict hypoglycemia within the next 24 hours 1

Hyperglycemia Thresholds

• Mild hyperglycemia: >180 mg/dL (10.0 mmol/L) 1, 2
• Significant hyperglycemia: >250 mg/dL (13.9 mmol/L) 2
• Severe hyperglycemia: >300 mg/dL (16.7 mmol/L) - requires evaluation for diabetic emergencies 2

Continuous Glucose Monitoring (CGM) vs. Fingerstick

• CGM measures interstitial glucose rather than capillary blood glucose 1, 5
• Time in range (70-180 mg/dL) has emerged as a key metric for glycemic control with CGM 5
• CGM may underestimate plasma glucose by an average of 12.8 mg/dL compared to laboratory measurements 6
• Fingerstick measurements are generally more accurate than CGM when compared to laboratory gold standards (MARD: 8.0% vs. 13.7%) 6

Key Takeaways

1. The standard normal range for fingerstick blood glucose is 90-150 mg/dL for fasting/pre-meal and up to 180 mg/dL for post-meal measurements.
2. Target ranges should be adjusted based on clinical context, age, and comorbidities.
3. Be aware of factors that can affect fingerstick accuracy, particularly in patients with poor peripheral circulation.
4. When in doubt about the accuracy of fingerstick measurements, confirm with laboratory testing, especially at extreme high or low values.