What are the indications for insulin therapy?

Indications for Insulin Therapy

Insulin therapy should be initiated immediately in patients with type 2 diabetes presenting with blood glucose ≥300 mg/dL, HbA1c ≥10%, or any level of hyperglycemia accompanied by catabolic features (weight loss, ketosis, hypertriglyceridemia) or symptomatic hyperglycemia (polyuria, polydipsia). 1, 2

Absolute Indications for Insulin

Type 1 Diabetes

• All patients with type 1 diabetes require insulin as primary treatment from diagnosis. 3, 4 This is non-negotiable as these patients have no endogenous insulin secretion.

Type 2 Diabetes - Immediate Initiation Required

Severe Hyperglycemia:

• Blood glucose consistently ≥300 mg/dL (≥16.7 mmol/L) 1, 2
• HbA1c ≥10% (≥86 mmol/mol) 1, 4
• HbA1c ≥9% with symptomatic hyperglycemia 5

Catabolic Features Present:

• Unexplained weight loss 1
• Ketosis or ketonuria 6, 5
• Hypertriglyceridemia 1

Symptomatic Hyperglycemia:

• Polyuria (excessive urination) 1
• Polydipsia (excessive thirst) 1

Type 2 Diabetes - Delayed Initiation

When oral agents fail after adequate trial:

• HbA1c remains above individualized target after 3 months of optimally titrated oral medications plus lifestyle modifications 1, 5
• Consider insulin when HbA1c ≥7.5% (≥58 mmol/mol) if oral agents are insufficient 4
• Definite consideration at HbA1c ≥9% even without symptoms 5

Special Clinical Circumstances

Acute medical conditions:

• Acute illness or surgery 4
• Pregnancy in patients with diabetes 4, 7
• Glucose toxicity requiring rapid normalization 4

Contraindications or failure of other therapies:

• Contraindications to oral antidiabetic medications 4
• Need for flexible therapy that oral agents cannot provide 4

Practical Implementation Algorithm

Step 1: Assess Severity at Presentation

If ANY of the following are present, start insulin immediately:

• Random glucose ≥300 mg/dL 2, 6, 5
• HbA1c ≥10% 1
• Weight loss, ketosis, or other catabolic features 1
• Symptomatic hyperglycemia (polyuria/polydipsia) 1

Step 2: Initial Insulin Regimen Selection

Start with basal insulin as first-line approach:

• Dose: 10 units once daily OR 0.1-0.2 units/kg/day 1, 2, 6
• For severe presentations (glucose >300 mg/dL): consider 0.2-0.3 units/kg/day 6, 5
• Timing: typically at bedtime 6, 8
• Always continue metformin unless contraindicated 1, 2, 6, 5

Preferred basal insulin options:

• Long-acting analogs (glargine, detemir, degludec) are preferred over NPH insulin due to 30-40% lower nocturnal hypoglycemia risk 1, 6, 4
• NPH insulin remains a more affordable alternative for cost-constrained patients 1

Step 3: Titration Strategy

Increase basal insulin systematically:

• Titrate every 3-4 days based on fasting glucose 2, 5
• Increase by 2-4 units per adjustment 1, 2, 5
• Target fasting glucose: 80-130 mg/dL (4.4-7.2 mmol/L) 2, 5
• Alternative: increase by 10-15% of current dose once or twice weekly 1

Step 4: Advancing Therapy When Basal Insulin Insufficient

Add prandial insulin when:

• Basal insulin dose >0.5 units/kg/day and HbA1c remains above target 1
• Fasting glucose controlled but HbA1c elevated 1

Prandial insulin initiation:

• Start with 4 units per meal OR 0.1 units/kg per meal OR 10% of basal dose per meal 1
• Rapid-acting analogs (lispro, aspart, glulisine) preferred for quick onset 1
• Consider decreasing basal insulin by equivalent amount when adding significant prandial doses 1

Critical Management Principles

Medication Continuation

• Metformin must be continued when starting insulin (reduces insulin requirements by 30-40%, limits weight gain by 2-3 kg, decreases hypoglycemia risk) 6, 4
• Other oral agents may be discontinued individually to avoid complex regimens 1
• Sulfonylureas should be discontinued when advancing to complex insulin regimens 6

Monitoring Requirements

• Fasting glucose guides basal insulin titration 1, 4
• Pre-meal and 2-hour postprandial glucose guide prandial insulin adjustments 6, 4
• HbA1c every 3 months to assess overall control 6, 5

Target Goals

• HbA1c <7% for most patients 2, 6, 5
• Fasting glucose 80-130 mg/dL 2, 5
• 2-hour postprandial glucose <180 mg/dL 5

Common Pitfalls to Avoid

Clinical inertia is dangerous:

• Delaying insulin when clearly indicated worsens beta-cell function and increases complication risk 6
• Recommendation for treatment intensification should not be delayed 1

Psychological barriers:

• Never use insulin as a threat or describe it as personal failure or punishment 1, 2, 6
• Frame insulin as natural disease progression requiring appropriate treatment 1, 2, 6
• The progressive nature of type 2 diabetes should be regularly and objectively explained 1

Overbasalization:

• Watch for clinical signals: basal dose >0.5 units/kg/day, high bedtime-morning glucose differential (≥50 mg/dL), hypoglycemia, high glycemic variability 1
• These signals should prompt reevaluation and consideration of adding prandial insulin rather than further increasing basal doses 1

Abrupt medication changes:

• Do not abruptly discontinue oral medications when starting insulin due to risk of rebound hyperglycemia 4

Special Insulin Formulations

Concentrated Insulins

• U-500 regular insulin: indicated for patients requiring >200 units/day 1
• U-300 glargine and U-200 degludec: allow higher basal doses per volume with longer duration 1

Inhaled Insulin

• Available for prandial use with limited dosing range 1
• Contraindicated in chronic lung disease (asthma, COPD) 1
• Not recommended for smokers or recent ex-smokers 1
• Requires spirometry before and after initiation 1

Premixed Insulins

• Contain fixed proportions of basal and prandial insulin 1
• Require relatively fixed meal schedule and carbohydrate content 1
• Option for patients benefiting from simpler dosing 1