What are the indications for insulin therapy?

Insulin Therapy Indications

Insulin therapy should be initiated immediately in patients with type 2 diabetes when random glucose ≥300 mg/dL, HbA1c ≥10%, or when hyperglycemia presents with catabolic features (unexplained weight loss, ketosis) or classic symptoms (polyuria, polydipsia). 1, 2

Immediate Initiation Criteria

Type 1 Diabetes:

• All patients with type 1 diabetes require insulin as primary treatment to sustain life and control blood glucose 3
• Initiate multiple daily injections at diagnosis, typically combining rapid-acting insulin before meals with intermediate or long-acting basal insulin 3

Type 2 Diabetes - Urgent Scenarios:

• Random plasma glucose ≥300 mg/dL 1
• HbA1c ≥10% (≥86 mmol/mol) 1, 2, 3
• HbA1c >9.0% or fasting plasma glucose ≥11.1 mmol/L with symptomatic hyperglycemia 4, 2
• Presence of catabolic features: unexplained weight loss, ketosis, or hypertriglyceridemia 1
• Classic hyperglycemic symptoms: polyuria and polydipsia 1, 2

Special Clinical Situations:

• Diabetic ketoacidosis (DKA) or nonketotic hyperosmolar state 4
• Perioperative period (preoperative, intraoperative, postoperative care) 4
• Post-cardiac surgery or organ transplantation 4
• Critical illness, cardiogenic shock, or sepsis 4
• High-dose glucocorticoid therapy causing exacerbated hyperglycemia 4
• Type 1 diabetic patients who are NPO 4
• Pregnancy in patients with diabetes requiring improved glycemic control 4
• Acute illness or surgery in type 2 diabetes patients 3
• Glucose toxicity requiring rapid correction 3

Delayed Initiation After Optimized Therapy

For Type 2 Diabetes:

• Add insulin when HbA1c remains above individualized target after ≥3 months of maximally titrated oral antidiabetic agents plus lifestyle modifications 1, 2
• Strongly consider insulin when HbA1c reaches ≥9% (≥75 mmol/mol) even without overt symptoms 1
• Essential when HbA1c ≥7.5% (≥58 mmol/mol) and oral agents have been optimally used 3
• Initiate within 3 months of recognizing failure of lifestyle intervention and oral medication combinations 4

Practical Initiation Strategy

Starting Regimen:

• Begin with basal insulin: either fixed dose of 10 units once daily or weight-based 0.1-0.2 units/kg/day 1, 2
• Continue metformin concurrently unless contraindicated, as it reduces insulin requirements by 30-40% and mitigates weight gain 1, 3
• Prefer long-acting insulin analogs (glargine, detemir, degludec) over NPH because they reduce nocturnal hypoglycemia risk by 30-40% 1
• NPH insulin remains acceptable when affordability is a concern 1

Titration Approach:

• Increase basal insulin by 2-4 units every 3-4 days based on fasting glucose readings targeting 80-130 mg/dL 1, 2
• Add prandial insulin when basal dose exceeds 0.5 units/kg/day and HbA1c remains above target 1
• Initiate prandial insulin with 4 units per meal or 0.1 units/kg per meal 1
• Use rapid-acting insulin analogs (lispro, aspart, glulisine) for prandial dosing 1

Alternative Intensive Approach:

• Short-term intensive insulin treatment (2 weeks to 3 months) may be implemented in newly diagnosed type 2 diabetes patients with HbA1c >9.0% or fasting plasma glucose ≥11.1 mmol/L 4
• Multiple daily insulin injections (2-4 injections per day) or continuous subcutaneous insulin infusion (CSII) are available options 4

Specialized Formulations and Delivery

High-Dose Requirements:

• U-500 regular insulin is indicated for patients requiring >200 units/day 1
• U-300 glargine and U-200 degludec allow higher basal doses in smaller volumes 1

Alternative Delivery Methods:

• Continuous subcutaneous insulin infusion (CSII) is appropriate for highly motivated patients who understand pump mechanics, perform self-monitoring, and desire lifestyle flexibility 4
• CSII can help improve metabolic control during pregnancy 4
• Inhaled rapid-acting insulin may be used for prandial coverage but is contraindicated in chronic lung disease (asthma, COPD), current or recent smokers, and requires spirometry monitoring 1
• Premixed insulin preparations suit patients with consistent meal timing and carbohydrate intake 1

Critical Communication Points

Avoid Common Pitfalls:

• Never present insulin as a threat, punishment, or personal failure; frame it as a natural progression requiring appropriate therapy 1, 2
• Do not abruptly discontinue oral medications when starting insulin due to risk of rebound hyperglycemia 3
• Recognize over-basalization signals: basal insulin >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, frequent hypoglycemia, or marked glycemic variability 1

Safety Considerations:

• Insulin glargine is not recommended for treatment of diabetic ketoacidosis 5
• Undetected interruptions in insulin delivery with CSII may result in ketotic episodes more quickly than with injections 4
• Use shortest needles (4-mm pen, 6-mm syringe) to avoid intramuscular injections and reduce pain 3
• Rotate injection sites properly to prevent lipohypertrophy, which distorts insulin absorption 3