When should insulin therapy be initiated in patients with diabetes?

When to Start Insulin Therapy in Diabetes

Insulin therapy should be initiated immediately in all patients with type 1 diabetes, in type 2 diabetes patients with severe hyperglycemia (blood glucose ≥250 mg/dL, A1C ≥8.5%), ketosis/ketoacidosis, or when the distinction between type 1 and type 2 diabetes is unclear. 1

Type 1 Diabetes

• Insulin is the mainstay of therapy for all individuals with type 1 diabetes and should be started at diagnosis 1
• Most patients require multiple daily injections of prandial and basal insulin or continuous subcutaneous insulin infusion 1
• Initial insulin dosage typically ranges from 0.4 to 1.0 units/kg/day of total insulin, with 0.5 units/kg/day as a typical starting dose for metabolically stable patients 1
• Higher weight-based dosing may be required following presentation with ketoacidosis 1

Type 2 Diabetes

Insulin initiation in type 2 diabetes depends on several clinical factors:

Immediate Insulin Initiation Required:

• Patients with ketosis or ketoacidosis 1
• Random blood glucose ≥250 mg/dL or A1C ≥8.5% with symptoms (polyuria, polydipsia, nocturia, weight loss) 1
• Very high blood glucose (≥300-350 mg/dL) or A1C ≥10% with symptomatic or catabolic features 1
• When the distinction between type 1 and type 2 diabetes is unclear 1

Consider Insulin Initiation:

• Evidence of ongoing catabolism (weight loss) 1
• When A1C remains above target despite optimal oral medication therapy 1
• During periods of acute illness, surgery, pregnancy, or when oral agents are contraindicated 2

Insulin Initiation Approaches

For Type 1 Diabetes:

• Begin with multiple daily injections of prandial and basal insulin or continuous subcutaneous insulin infusion 1
• Rapid-acting insulin analogs are preferred to reduce hypoglycemia risk 1
• Consider education on matching prandial insulin doses to carbohydrate intake, premeal glucose levels, and anticipated physical activity 1

For Type 2 Diabetes:

• Initial approach: Start with basal insulin (typically 10 units or 0.1-0.2 units/kg/day) while continuing metformin 1
• For those with marked hyperglycemia (blood glucose ≥250 mg/dL, A1C ≥8.5%), start basal insulin while initiating and titrating metformin 1
• For severe hyperglycemia with symptoms or catabolic features, consider basal insulin plus mealtime insulin 1
• When basal insulin has been titrated to appropriate fasting glucose but A1C remains above target, consider adding prandial insulin or GLP-1 receptor agonist 1

Special Considerations

• Monitoring: Frequent blood glucose monitoring is essential when starting insulin therapy 2
• Hypoglycemia risk: Use of insulin analogs rather than regular human insulin reduces risk of hypoglycemia, especially nocturnal episodes 2, 3
• Combination therapy: Metformin should generally be continued when starting insulin in type 2 diabetes as it is associated with decreased weight gain, lower insulin dose requirements, and less hypoglycemia 2
• Hospitalized patients: For inpatients, a basal plus correction insulin regimen is preferred for those with poor oral intake, while a regimen with basal, nutritional, and correction components is preferred for those with good nutritional intake 1

Common Pitfalls to Avoid

• Therapeutic inertia: Delaying insulin initiation when clearly indicated can lead to prolonged hyperglycemia and increased risk of complications 1
• Sole use of sliding scale insulin: This approach is strongly discouraged in the inpatient setting 1
• Abrupt discontinuation of oral medications: When starting insulin therapy, oral medications should not be abruptly discontinued due to risk of rebound hyperglycemia 2
• Inadequate monitoring: Blood glucose monitoring is integral to effective insulin therapy; fasting values should be used to titrate basal insulin, while both fasting and postprandial values should guide mealtime insulin adjustments 2

By following these evidence-based guidelines for insulin initiation, clinicians can optimize glycemic control and potentially reduce the risk of diabetes-related complications while minimizing adverse effects such as hypoglycemia.