At what point should insulin be added for a type 2 diabetic?

When to Add Insulin for Type 2 Diabetes

Insulin should be initiated immediately at diagnosis when blood glucose is ≥300 mg/dL or HbA1c is ≥10%, especially if the patient has symptoms of hyperglycemia (polyuria, polydipsia, weight loss) or evidence of catabolism. 1

Immediate Insulin Initiation Criteria

Start insulin at diagnosis if any of the following are present:

• Blood glucose ≥300-350 mg/dL 1
• HbA1c ≥10% (86 mmol/mol) 1
• Symptomatic hyperglycemia (polyuria, polydipsia, nocturia, weight loss) 1
• Evidence of catabolism (unintentional weight loss, hypertriglyceridemia, ketosis) 1

In these situations, insulin therapy should be started with or without additional agents to rapidly correct glucose toxicity. 1 Once metabolic stabilization occurs, the regimen can often be simplified or transitioned to oral agents. 1

Insulin After Oral Agent Failure

Add basal insulin when:

• HbA1c remains above target after 3 months on metformin plus one or two additional oral agents 1
• Metformin contraindications or intolerance develop and HbA1c is not at goal 1
• HbA1c is 1.5-2.0% above target despite dual oral therapy 1

The American Diabetes Association guidelines emphasize that basal insulin should be added when oral agents fail to maintain glycemic control, typically when HbA1c exceeds 7% on maximally tolerated doses. 1

Special Populations

For youth with type 2 diabetes:

• Start basal insulin if HbA1c ≥8.5% (69 mmol/mol) with symptoms (blood glucose ≥250 mg/dL) while initiating metformin 1
• Use insulin plus metformin for ketosis/ketoacidosis at presentation 1

Practical Implementation

Initial basal insulin dosing:

• Start with 10 units daily or 0.1-0.2 units/kg depending on hyperglycemia severity 1
• Titrate by 2-4 units every 3-7 days until fasting glucose reaches target (80-130 mg/dL) 1, 2
• Continue metformin when adding insulin to reduce insulin requirements and minimize weight gain 1

If basal insulin alone is insufficient (dose >0.5 units/kg/day or HbA1c still above target):

• Add one injection of rapid-acting insulin before the largest meal (starting at 4 units or 10% of basal dose) 1, 2
• Alternatively, add a GLP-1 receptor agonist (associated with weight loss and less hypoglycemia but higher cost) 1
• Or switch to twice-daily premixed insulin 1

Common Pitfalls to Avoid

Do not delay insulin when clearly indicated. Prolonged exposure to severe hyperglycemia (HbA1c >9% for months) increases complication risk and should be specifically avoided. 2 The progressive nature of type 2 diabetes means most patients will eventually require insulin, and it should not be presented as a failure or punishment. 1

Avoid relying solely on sliding-scale insulin without optimizing basal insulin first—this approach is ineffective for long-term management. 2

Do not add a third oral agent when HbA1c is ≥10% without concurrent insulin therapy, as oral agents typically reduce HbA1c by only 0.7-1.0% each. 1, 2

Weight and Hypoglycemia Considerations

Insulin therapy causes weight gain (average 1.9-3.7 kg), which can be minimized by continuing metformin and considering addition of GLP-1 receptor agonists or SGLT2 inhibitors. 1 Sulfonylureas should typically be discontinued when advancing to complex insulin regimens beyond basal insulin to reduce hypoglycemia risk. 1, 2