How do I adjust my insulin doses according to my random blood sugar levels?

Insulin Dosing Based on Random Blood Sugar Levels

Initial Insulin Dosing Strategy

For type 2 diabetes patients requiring insulin therapy, start with basal insulin at 10 units once daily or 0.1-0.2 units/kg body weight, administered at the same time each day, and titrate based on fasting blood glucose—not random blood sugar levels. 1, 2, 3

Key Principle: Match Insulin Type to Blood Glucose Pattern

• Basal insulin (Lantus/glargine) addresses fasting and between-meal glucose levels, not random or postprandial spikes 2
• Prandial insulin (rapid-acting) addresses meal-related glucose excursions and should be adjusted based on pre-meal and 2-hour postprandial readings 1, 2
• Random blood sugar levels reflect a combination of basal and prandial insulin adequacy, making them unreliable for systematic dose adjustments 2

Evidence-Based Titration Algorithm for Basal Insulin

Adjust Based on Fasting Glucose (Not Random Readings)

Increase basal insulin dose every 3 days based on fasting plasma glucose:

• If fasting glucose 140-179 mg/dL: increase by 2 units 1, 2
• If fasting glucose ≥180 mg/dL: increase by 4 units 1, 2
• Target fasting glucose: 80-130 mg/dL 1, 2
• If hypoglycemia occurs without clear cause, reduce dose by 10-20% immediately 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, add prandial insulin rather than continuing to escalate basal insulin alone. 1, 2 This prevents "overbasalization"—a dangerous pattern where excessive basal insulin masks inadequate mealtime coverage 2.

Clinical signals of overbasalization include:

• Basal insulin dose >0.5 units/kg/day 2
• Bedtime-to-morning glucose differential ≥50 mg/dL 2
• Hypoglycemia episodes 2
• High glucose variability 2

Adding Prandial Insulin for Persistent Hyperglycemia

When Random Blood Sugars Remain Elevated Despite Optimal Basal Insulin

If fasting glucose reaches target (80-130 mg/dL) but A1C remains above goal after 3-6 months, or if random/postprandial glucose readings are consistently elevated, add prandial insulin. 1, 2

Prandial Insulin Initiation

• Start with 4 units of rapid-acting insulin before the largest meal or the meal causing greatest glucose excursion 1, 2
• Alternative: use 10% of current basal dose as starting prandial dose 1, 2
• Increase prandial insulin by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose readings 1, 2

Practical Correction Insulin ("Sliding Scale") Guidelines

Using Correction Doses for Elevated Random Blood Sugars

While systematic insulin adjustments should be based on fasting and postprandial patterns, correction insulin can address acute hyperglycemic excursions 2:

• Calculate insulin sensitivity factor (ISF) = 1500 ÷ total daily insulin dose 2
• For each 1 unit of rapid-acting insulin, expect blood glucose to drop by the ISF amount 2
• Example: If ISF = 50 mg/dL per unit, and random glucose is 250 mg/dL with target 150 mg/dL, give 2 units correction dose 2

Critical caveat: Correction insulin addresses acute elevations but does not replace the need for proper basal and prandial insulin titration 2. Relying solely on correction insulin leads to suboptimal control 2.

Monitoring Requirements During Titration

• Daily fasting blood glucose monitoring is essential during the titration phase 1, 2
• Check pre-meal glucose and 2-hour postprandial glucose to evaluate insulin adequacy 4
• Reassess insulin doses every 3-6 months to avoid therapeutic inertia 1, 2

Common Pitfalls to Avoid

Do Not Use Random Blood Sugars for Systematic Basal Insulin Adjustment

Fasting glucose reflects basal insulin adequacy; random or postprandial glucose reflects prandial insulin adequacy. 2 Adjusting basal insulin based on random readings leads to overbasalization and increased hypoglycemia risk 2.

Do Not Continue Escalating Basal Insulin Beyond 0.5-1.0 units/kg/day

When basal insulin approaches this threshold without achieving glycemic targets, add prandial insulin rather than continuing to increase basal doses. 1, 2 This prevents excessive basal insulin that masks inadequate mealtime coverage 2.

Do Not Delay Adding Prandial Insulin

Blood glucose levels consistently in the 200s mg/dL indicate both inadequate basal coverage AND postprandial excursions requiring mealtime insulin. 2 Continuing to increase only basal insulin in this scenario leads to suboptimal control 2.

Foundation Therapy

Continue metformin (unless contraindicated) when initiating or intensifying insulin therapy, as it reduces total insulin requirements and provides complementary glucose-lowering effects 1, 2, 4. The typical effective dose is 1000 mg twice daily, with maximum benefit up to 2500 mg/day 4.

Special Considerations for Severe Hyperglycemia

For patients with A1C ≥10-12% with symptomatic or catabolic features, or blood glucose ≥300-350 mg/dL, start basal-bolus insulin immediately rather than basal insulin alone 1, 2. Use total daily dose of 0.3-0.5 units/kg/day, split 50% basal and 50% prandial 1, 2.