When should insulin be used in patients with hyperglycemia?

When Should Insulin Be Used?

Insulin should be initiated when blood glucose persistently exceeds 180 mg/dL (10.0 mmol/L) in hospitalized patients, or when HbA1c is ≥9% in outpatients with type 2 diabetes, particularly if symptomatic hyperglycemia or catabolic features are present. 1

Outpatient/Ambulatory Settings

Type 1 Diabetes

• Insulin is the primary and essential treatment for all patients with type 1 diabetes from the time of diagnosis 2
• Multiple daily injections are required: rapid-acting insulin 0-15 minutes before meals plus one or more daily injections of basal insulin 2
• Insulin must never be discontinued in type 1 diabetes patients 1

Type 2 Diabetes - Clear Thresholds for Starting Insulin

Start insulin immediately when: 1

• Blood glucose ≥300-350 mg/dL (16.7-19.4 mmol/L) AND/OR
• HbA1c ≥10-12%, especially with symptoms (weight loss, polyuria, polydipsia) or catabolic features
• In these severe cases, use basal insulin PLUS mealtime insulin from the start 1

Consider adding basal insulin when: 1, 3

• HbA1c ≥9% despite one or two oral medications or one oral agent plus GLP-1 receptor agonist
• Patient has symptomatic hyperglycemia despite oral agents
• Contraindications exist to oral medications 2

Starting dose for insulin-naive type 2 diabetes patients: 4

• 0.2 units/kg body weight OR up to 10 units once daily of basal insulin
• Alternatively, 0.3-0.5 units/kg total daily dose when using basal-bolus regimen 1

Hospitalized Patients

Critical Care/ICU Settings

Initiate intravenous insulin infusion when: 1, 5

• Blood glucose ≥180 mg/dL on two separate occasions
• Target glucose range: 140-180 mg/dL for most critically ill patients
• More stringent targets (110-140 mg/dL) may be appropriate for cardiac surgery patients using computerized algorithms that minimize hypoglycemia risk 1

Avoid targets <110 mg/dL - the NICE-SUGAR trial demonstrated increased mortality with intensive control (80-110 mg/dL) compared to moderate targets (140-180 mg/dL), with 10-15 fold higher hypoglycemia rates 1

Non-Critical Care Hospital Settings

Use scheduled subcutaneous insulin (not sliding scale alone) when: 1

• Blood glucose persistently >140 mg/dL
• Patient has known diabetes requiring insulin at home
• Patient is NPO or has poor oral intake (use basal insulin or basal-plus-correction regimen) 1
• Patient is eating regular meals (use basal-bolus-correction regimen) 1

Basal-bolus regimen specifics: 1

• Give 50% of total daily dose as basal insulin (once or twice daily)
• Give 50% as rapid-acting insulin divided before three meals
• Add correction doses as needed
• For insulin-naive patients: start with 0.3-0.5 units/kg/day total 1
• For patients on high-dose insulin at home (≥0.6 units/kg/day): reduce by 20% to prevent hypoglycemia 1

Emergency/Acute Situations

Start continuous IV insulin immediately for: 6

• Diabetic ketoacidosis or hyperosmolar hyperglycemic state
• Blood glucose >900 mg/dL (50 mmol/L) with altered mental status, severe dehydration, or Kussmaul respirations 6
• Begin at 0.1 units/kg/hour (typically 5-10 units/hour) using regular insulin 6

Critical safety consideration: Check serum potassium before starting insulin - if K+ <3.3 mEq/L, hold insulin and replace potassium first, as severe hypokalemia occurs in ~50% of hyperglycemic crises and increases mortality 6

Common Pitfalls to Avoid

• Never use sliding scale insulin alone in hospitalized patients with established diabetes - it is associated with poor glycemic control and is strongly discouraged 1
• Do not delay insulin when clearly indicated - timely initiation improves outcomes 1
• Avoid abrupt discontinuation of oral medications when starting insulin due to rebound hyperglycemia risk 2
• Do not target glucose <110 mg/dL in critically ill patients - this increases mortality 1
• Check potassium levels before initiating insulin in hyperglycemic emergencies 6