What is a tolerable fasting blood sugar (FBS) level for maintenance in individuals with known diabetes mellitus?

Tolerable Fasting Blood Sugar for Maintenance in Known Diabetes Mellitus

For most adults with known diabetes mellitus, the target fasting blood sugar should be 80-130 mg/dL (4.4-7.2 mmol/L), though this must be adjusted based on patient age, health complexity, and hypoglycemia risk. 1

Standard Targets for Most Adults with Diabetes

• Fasting/preprandial glucose target: 80-130 mg/dL (4.4-7.2 mmol/L) is recommended for the majority of non-pregnant adults with diabetes 1

• This target correlates with achieving an HbA1c <7.0% (53 mmol/mol), which reduces microvascular complications 1

• Peak postprandial glucose should remain <180 mg/dL (10.0 mmol/L) to complement fasting control 1

Age-Stratified and Health Status-Based Targets

Healthy Older Adults (Few Comorbidities, Intact Function)

• Fasting glucose: 80-130 mg/dL (4.4-7.2 mmol/L) 1
• These patients can tolerate more stringent goals similar to younger adults 1

Complex/Intermediate Health Older Adults (Multiple Comorbidities or Mild-Moderate Cognitive Impairment)

• Fasting glucose: 90-150 mg/dL (5.0-8.3 mmol/L) 1
• This relaxed target reduces hypoglycemia risk while preventing acute hyperglycemic complications 1

Very Complex/Poor Health Older Adults (End-Stage Illness, Severe Cognitive Impairment, ADL Dependence)

• Fasting glucose: 100-180 mg/dL (5.6-10.0 mmol/L) 1
• The primary goal shifts to avoiding symptomatic hyperglycemia (dehydration, poor wound healing) and hypoglycemia rather than achieving tight control 1

More Stringent Targets (When Appropriate)

• Fasting glucose: 110-140 mg/dL (6.1-7.8 mmol/L) may be appropriate for selected patients with: 1
  • Short diabetes duration
  • Long life expectancy
  • No significant cardiovascular disease
  • No history of severe hypoglycemia
  • Ability to achieve targets without significant hypoglycemia 1

Hospitalized Patients

• Target range: 140-180 mg/dL (7.8-10.0 mmol/L) for both critically ill and non-critically ill hospitalized patients 1

• More stringent hospital targets of 100-180 mg/dL (5.6-10.0 mmol/L) are acceptable for non-critically ill patients if achievable without hypoglycemia 1

• Insulin therapy should be initiated when glucose persistently exceeds 180 mg/dL (10.0 mmol/L) 1

Critical Hypoglycemia Thresholds to Avoid

• Glucose <70 mg/dL (3.9 mmol/L) requires immediate treatment with 15-20g of fast-acting carbohydrate 1

• Glucose <54 mg/dL (3.0 mmol/L) represents clinically significant hypoglycemia with neuroglycopenic symptoms requiring urgent intervention 1

• Fasting glucose <100 mg/dL predicts hypoglycemia risk within 24 hours in hospitalized patients 1

Key Factors for Individualizing Targets

When determining the appropriate fasting glucose target, consider: 1

• Duration of diabetes: Longer duration may warrant less stringent goals due to accumulated complications
• Life expectancy: Shorter life expectancy favors less aggressive targets (time to benefit from tight control exceeds remaining lifespan)
• Hypoglycemia history: Any history of severe hypoglycemia or hypoglycemia unawareness mandates higher targets
• Comorbidities: Advanced microvascular/macrovascular complications, heart failure, chronic kidney disease stage 3+, or multiple chronic conditions warrant relaxed targets 1
• Cognitive/functional status: Impaired cognition or ADL dependence increases hypoglycemia risk and reduces ability to recognize/treat low glucose 1

Common Pitfalls to Avoid

• Do not apply uniform targets across all patients: A 75-year-old with dementia and heart failure should not have the same 80-130 mg/dL target as a healthy 45-year-old 1

• Avoid over-reliance on A1C in very complex patients: Focus on avoiding symptomatic hyperglycemia rather than achieving specific A1C targets in end-stage illness 1

• Do not ignore hypoglycemia risk: Targets below 100 mg/dL significantly increase hypoglycemia risk, particularly in older adults and those on insulin or sulfonylureas 1

• Recognize that "normal" fasting glucose (70-99 mg/dL) is not appropriate for most patients with established diabetes on glucose-lowering medications: This increases hypoglycemia risk without proven additional benefit 1, 2

• Reassess targets regularly: Health status changes over time, requiring adjustment of glucose targets 1