How do I adjust my insulin dosage based on blood glucose readings?

Adjusting Insulin Based on Blood Glucose Readings

Adjust your insulin systematically by increasing basal insulin by 2-4 units every 3 days based on fasting glucose readings, and add prandial insulin when basal insulin exceeds 0.5 units/kg/day or when postprandial hyperglycemia persists despite controlled fasting glucose. 1, 2

Basal Insulin Titration Algorithm

For patients on basal insulin (such as Lantus, Toujeo, or Tresiba), use the following evidence-based titration schedule:

• If fasting glucose ≥180 mg/dL: Increase basal insulin by 4 units every 3 days until reaching target 1, 2
• If fasting glucose 140-179 mg/dL: Increase basal insulin by 2 units every 3 days 1, 2
• If fasting glucose 80-130 mg/dL: Maintain current basal insulin dose—this is your target range 1, 2
• If >2 fasting values per week <80 mg/dL: Decrease basal insulin by 2 units to prevent hypoglycemia 1, 2

The American Diabetes Association emphasizes that basal insulin should be titrated based exclusively on fasting plasma glucose values, as these reflect basal insulin adequacy rather than meal coverage 1, 2. Daily self-monitoring of fasting blood glucose is essential during this titration phase 1, 2.

Critical Threshold: When to Stop Escalating Basal Insulin

When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, stop increasing basal insulin and add prandial insulin instead. 1, 2 Continuing to escalate basal insulin beyond this threshold leads to "overbasalization"—a dangerous pattern where excessive basal insulin masks the need for mealtime coverage 1.

Clinical signals of overbasalization include 1:

• Basal insulin dose >0.5 units/kg/day
• Bedtime-to-morning glucose differential ≥50 mg/dL
• Hypoglycemia episodes
• High glucose variability

Adding Prandial (Mealtime) Insulin

When fasting glucose is controlled (80-130 mg/dL) but A1C remains above target after 3-6 months, or when blood glucose readings remain elevated throughout the day, add prandial insulin: 1, 2

• Start with 4 units of rapid-acting insulin (such as Humalog, NovoLog, or Apidra) before the largest meal or the meal causing the greatest postprandial glucose excursion 1, 2
• Alternative starting dose: Use 10% of your current basal insulin dose 1, 2
• Administer rapid-acting insulin 0-15 minutes before meals for optimal postprandial glucose control 1, 3, 4

Titrate prandial insulin by 1-2 units (or 10-15%) every 3 days based on pre-meal and 2-hour postprandial glucose readings 1, 2. The American Diabetes Association recommends checking 2-hour postprandial glucose after the largest meal to guide these adjustments 2, 3.

Monitoring Requirements

Essential glucose monitoring during insulin adjustment includes: 2, 3

• Daily fasting glucose to guide basal insulin titration
• Pre-meal glucose before each meal when on prandial insulin
• 2-hour postprandial glucose after the largest meal to assess prandial insulin adequacy
• Reassess every 3 days during active titration
• Check A1C every 3 months until target is achieved

Research demonstrates that glucose readings alone are sufficient to adjust insulin dosage effectively and safely when adjustments are made every 1-4 weeks, with software-based recommendations showing 95-99% clinical equivalence to endocrinologist decisions 5, 6.

Hypoglycemia Management

If hypoglycemia occurs (glucose <70 mg/dL): 2, 3

• Treat immediately with 15-20 grams of fast-acting carbohydrate
• Recheck glucose in 15 minutes and repeat treatment if still hypoglycemic
• Reduce the relevant insulin dose by 10-20% immediately 1, 2
• Determine the cause before resuming titration
• Carry at least 15 grams of carbohydrate at all times

Foundation Therapy Considerations

Continue metformin when adding or intensifying insulin therapy unless contraindicated. 1, 2, 3 Metformin combined with insulin is associated with decreased weight gain, lower insulin requirements, and less hypoglycemia compared to insulin alone 7. The American Diabetes Association recommends metformin as the foundation of type 2 diabetes therapy even during insulin intensification 1, 3.

Common Pitfalls to Avoid

• Do not delay insulin adjustments: Waiting longer than 3 days between basal insulin adjustments in stable patients unnecessarily prolongs time to glycemic targets 1
• Do not continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia—this leads to suboptimal control and increased hypoglycemia risk 1, 2
• Do not blame fasting hyperglycemia on missed meal coverage: Fasting glucose reflects basal insulin adequacy, not prandial insulin 1
• Do not use sliding scale insulin alone: Scheduled basal-bolus regimens with fixed prandial doses are superior to sliding scale monotherapy 3, 7
• Avoid using abbreviations like "U" for units when documenting insulin doses, as this can be misread as zero and cause 10-fold overdoses 8

Special Situations

For severe hyperglycemia (A1C ≥10-12% or blood glucose ≥300-350 mg/dL with symptoms): Start basal-bolus insulin immediately rather than basal insulin alone, using 0.3-0.5 units/kg/day as total daily dose, split 50% basal and 50% prandial 1, 3.

For hospitalized patients on high-dose home insulin (≥0.6 units/kg/day): Reduce total daily dose by 20% upon admission to prevent hypoglycemia 1, 2.

For patients on corticosteroids: Increase prandial and correction insulin by 40-60% or more in addition to basal insulin adjustments 1.