What is the ideal carb ratio for someone with a Neutral Protamine Hagedorn (NPH) insulin dose of 36 units?

Calculating Carbohydrate Ratio for NPH Insulin 36 Units

For a patient on 36 units of NPH insulin, the carbohydrate ratio should be calculated as 1:10 to 1:15 (meaning 1 unit of insulin covers 10-15 grams of carbohydrate), depending on the clinical context and patient characteristics. 1, 2

Standard Calculation Method

The carbohydrate-to-insulin ratio (CIR) is traditionally calculated from the total daily dose (TDD) of insulin using established formulas:

• For patients on insulin pump therapy or multiple daily injections: The standard formula is CIR = 500/TDD, though recent evidence suggests this may underestimate insulin needs 3
• More accurate calculations based on Japanese type 1 diabetes patients show CIR = 300/TDD for breakfast and CIR = 400/TDD for lunch and dinner, accounting for diurnal variation in insulin sensitivity 3

Applying This to 36 Units NPH

If 36 units represents your total daily insulin dose:

• Using the 500 rule: 500 ÷ 36 = 1:14 (1 unit per 14g carbohydrate)
• Using the more conservative 400 rule (for lunch/dinner): 400 ÷ 36 = 1:11 (1 unit per 11g carbohydrate)
• Using the 300 rule (for breakfast): 300 ÷ 36 = 1:8 (1 unit per 8g carbohydrate) 3

Context-Specific Adjustments

For Enteral Nutrition Patients

• The American Diabetes Association recommends 1 unit of insulin for every 10-15 grams of carbohydrate in enteral and parenteral formulas 1, 2
• For patients with obesity receiving enteral nutrition, use the more aggressive ratio of 1:10 2
• NPH should be given every 8-12 hours to cover nutritional requirements 1, 4

For Steroid-Induced Hyperglycemia

• Initial carbohydrate ratio of 1:8 is appropriate for patients on high-dose steroids with obesity, accounting for significant insulin resistance 5
• May need adjustment to 1:6 or 1:5 if persistent postprandial hyperglycemia occurs 5
• Patients on high-dose glucocorticoids often require 40-60% more insulin than standard dosing 1, 6

For Standard Basal-Bolus Regimens

• If NPH represents approximately 50% of total daily insulin (traditional approach), your TDD would be ~72 units, yielding a ratio of approximately 1:7 to 1:10 1
• However, basal insulin typically represents only 27-30% of TDD in well-controlled patients, suggesting NPH of 36 units implies a TDD of ~120 units and a ratio closer to 1:4 to 1:5 3

Practical Starting Point

Begin with a ratio of 1:10 (1 unit per 10g carbohydrate) and adjust based on blood glucose monitoring:

• If postprandial glucose consistently >180 mg/dL: Increase insulin (move toward 1:8 or 1:6) 1
• If experiencing hypoglycemia: Decrease insulin (move toward 1:12 or 1:15) 6
• Monitor blood glucose before meals and 2 hours postprandially to assess adequacy 5

Critical Considerations

• Carbohydrate ratios vary throughout the day: More insulin is typically needed per gram of carbohydrate at breakfast due to dawn phenomenon and counter-regulatory hormones 1, 3
• NPH insulin peaks 4-6 hours after administration, so timing of meals relative to NPH dosing is crucial 1, 6
• For patients with type 1 diabetes: Continue basal insulin even if meals are interrupted to prevent diabetic ketoacidosis 1, 2
• Adjust doses frequently based on blood glucose patterns—increase by 2 units every 3 days for persistent hyperglycemia, or decrease by 10-20% for hypoglycemia 6, 5

Common Pitfalls to Avoid

• Do not use the same ratio for all meals: Breakfast typically requires more insulin per gram of carbohydrate 3
• Account for patient-specific factors: Obesity, steroid use, and critical illness all increase insulin requirements significantly 1, 5
• If enteral nutrition is interrupted: Start dextrose infusion immediately to prevent hypoglycemia 1, 2