When to Start Insulin Therapy in Patients with Diabetes
Insulin therapy should be initiated immediately for all patients with type 1 diabetes, and for type 2 diabetes patients who have HbA1c ≥8.5%, significant hyperglycemia (≥250 mg/dL), or who present with symptoms such as ketosis, unintentional weight loss, or diabetic ketoacidosis. 1
Type 1 Diabetes
- Insulin is the mainstay of therapy for all individuals with type 1 diabetes 2
- Must be started at diagnosis
- Initial dosing:
- Starting dose typically 0.4-1.0 units/kg/day of total insulin 2
- American Diabetes Association suggests 0.5 units/kg/day as typical starting dose for metabolically stable patients 2
- Higher weight-based dosing required immediately following presentation with ketoacidosis 2
- Higher insulin doses often required during puberty 2
Type 2 Diabetes
Insulin initiation is indicated in the following scenarios:
Immediate Insulin Initiation Required:
- HbA1c ≥8.5% (69 mmol/mol) 2, 1
- Random blood glucose ≥250 mg/dL (13.9 mmol/L) 2
- Presence of ketosis or ketoacidosis 2, 3
- Symptomatic hyperglycemia with unintentional weight loss 1
- Acute illness or surgery requiring tight glucose control 3
- Pregnancy 3
Consider Insulin When:
- HbA1c ≥7.5% (58 mmol/mol) despite optimal use of other antihyperglycemic agents 3
- Glucose toxicity is present 3
- Contraindications to or failure to achieve goals with oral antidiabetic medications 3
Initial Insulin Regimens
For Type 1 Diabetes:
- Multiple daily injections (MDI) of prandial and basal insulin or continuous subcutaneous insulin infusion (CSII) 2
- Typically requires:
- Basal insulin: Once or twice daily
- Rapid-acting insulin: Before meals
- Total daily insulin requirements divided with approximately one-third as basal insulin 4
For Type 2 Diabetes:
- Recommended starting dosage for insulin-naïve patients: 0.2 units/kg or up to 10 units once daily 4
- Preferred methods for initiation 3:
- Add a long-acting (basal) insulin once daily
- Once-daily premixed/co-formulation insulin
- Twice-daily premixed insulin
- Can be used alone or in combination with GLP-1 receptor agonists or oral antidiabetic drugs
Insulin Titration and Monitoring
- Increase dose by 2 units every 3 days until fasting plasma glucose target is reached without hypoglycemia 1
- Monitor blood glucose before breakfast daily during titration 1
- If hypoglycemia occurs, determine the cause; if no clear reason, lower dose by 10-20% 1
- Consider more frequent monitoring in patients with decreased kidney function (eGFR <60 mL/min/1.73m²) 1
Special Considerations
Switching from Other Insulin Therapies
When switching from:
- Once-daily NPH insulin to once-daily insulin glargine: Use same dosage 4
- Twice-daily NPH insulin to once-daily insulin glargine: Use 80% of the total NPH dosage 4
- Insulin glargine 300 units/mL to insulin glargine 100 units/mL: Use 80% of the previous dosage 4
Older Adults
- Target fasting glucose range should be 90-150 mg/dL 1
- Consider less stringent HbA1c goals (such as <8%) for patients with limited life expectancy or extensive comorbidities 1
Common Pitfalls to Avoid
- Delayed insulin initiation: Postponing insulin in patients who clearly need it can lead to prolonged hyperglycemia and increased risk of complications
- Abrupt discontinuation of oral medications: When starting insulin therapy, oral medications should not be abruptly discontinued due to risk of rebound hyperglycemia 3
- Inadequate monitoring: Failing to increase monitoring frequency when changing insulin regimens can lead to undetected hypo- or hyperglycemia 4
- Inappropriate injection technique: Repeated insulin injections into areas of lipodystrophy can result in poor absorption and hyperglycemia 4
- Relying solely on correction insulin: Using only correction insulin without basal coverage leads to poor glycemic control 1
By following these evidence-based guidelines for insulin initiation, patients can achieve better glycemic control and reduce the risk of diabetes-related complications.