According to guidelines, what are the indications to initiate insulin therapy in a diabetic patient (including type 1 and type 2)?

Indications to Initiate Insulin Therapy in Diabetic Patients

Insulin therapy should be started immediately in type 1 diabetes at diagnosis, and in type 2 diabetes when HbA1c ≥9%, blood glucose ≥300 mg/dL, or when symptoms of hyperglycemia/catabolism are present.

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Type 1 Diabetes: Absolute Indications

Insulin is the primary and essential treatment for all patients with type 1 diabetes from the moment of diagnosis. 1

• Start multiple daily injections immediately at diagnosis with a basal-bolus regimen consisting of short-acting or rapid-acting insulin analogue given 0–15 minutes before meals, plus one or more daily injections of intermediate or long-acting insulin. 1
• Initial total daily dose is typically 0.4–1.0 units/kg/day, with approximately 50% as basal insulin and 50% as prandial insulin divided among meals. 2
• For metabolically stable patients, 0.5 units/kg/day is the typical starting point. 2
• Higher doses are required immediately following presentation with ketoacidosis. 3

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Type 2 Diabetes: Specific Indications for Insulin Initiation

Immediate/Urgent Indications (Start Insulin Now)

Insulin must be initiated immediately in the following scenarios:

• HbA1c ≥10% (≥86 mmol/mol) with symptomatic or catabolic features (unexpected weight loss, nausea, vomiting). 2, 1
• Blood glucose ≥300–350 mg/dL regardless of HbA1c. 2
• Evidence of ongoing catabolism such as unexpected weight loss. 2
• Symptoms of hyperglycemia including polyuria, polydipsia, or blurred vision. 2
• Acute illness, surgery, or pregnancy where oral agents are contraindicated. 1
• Glucose toxicity requiring rapid glycemic correction. 1

Strong Indications (Insulin Highly Recommended)

• HbA1c ≥9% (≥75 mmol/mol) even without symptoms—consider starting insulin earlier in the treatment algorithm. 2, 1
• HbA1c ≥7.5% (≥58 mmol/mol) despite optimal use of metformin and/or sulfonylurea. 2, 1
• Failure to achieve glycemic goals with oral antidiabetic medications after 3 months of optimal therapy. 4
• Contraindications to or failure of oral agents to achieve targets. 1

Relative Indications (Consider Insulin)

• HbA1c 7.5–9% when other glucose-lowering agents are unsuitable or insufficient. 2
• Fasting plasma glucose ≥11.1 mmol/L (≥200 mg/dL). 4
• Need for flexible therapy that oral agents cannot provide. 1

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Choosing the Initial Insulin Regimen

For Type 2 Diabetes with Moderate Hyperglycemia (HbA1c <9%)

Start with basal insulin alone:

• Begin with 10 units once daily or 0.1–0.2 units/kg/day of long-acting insulin (glargine, detemir, or degludec) at the same time each day. 2, 5
• Continue metformin unless contraindicated, and possibly one additional non-insulin agent. 2
• Titrate by 2–4 units every 3 days until fasting glucose reaches 80–130 mg/dL. 2

For Type 2 Diabetes with Severe Hyperglycemia (HbA1c ≥9% or glucose ≥300 mg/dL)

Start with basal-bolus insulin immediately:

• Total daily dose of 0.3–0.5 units/kg/day, split 50% basal and 50% prandial insulin divided among three meals. 2
• This approach provides both fasting and postprandial glucose control from the outset. 2

Alternative: Premixed Insulin

• Premixed insulin (e.g., 70/30) may be used 1–3 times daily as an alternative for short-term intensive therapy (2 weeks to 3 months) in newly diagnosed patients with severe hyperglycemia. 4
• However, premixed insulin is not recommended for hospitalized patients due to unacceptably high hypoglycemia rates. 2

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When NOT to Delay Insulin

Common pitfalls to avoid:

• Do not delay insulin initiation in patients not achieving glycemic goals with oral medications—this prolongs hyperglycemia exposure and increases complication risk. 2
• Do not wait for "failure" of multiple oral agents when HbA1c is already ≥9%—insulin should be started earlier. 2
• Insulin is not a "last resort"—it is the most effective glucose-lowering agent and should be used when clinically indicated. 2

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Special Populations

Children and Adolescents with Type 2 Diabetes

• Start basal insulin at 0.5 units/kg/day in addition to metformin when HbA1c >8.5% without acidosis or ketosis. 3
• Target HbA1c for children with type 1 diabetes is <7.5% (<58 mmol/mol). 1

Hospitalized Patients

• For non-critically ill hospitalized patients, start basal-bolus insulin at 0.3–0.5 units/kg/day (50% basal, 50% prandial) when eating regular meals. 2
• For high-risk patients (elderly >65 years, renal impairment, poor oral intake), use lower doses of 0.1–0.25 units/kg/day. 2

Patients on Continuous Tube Feeding

• Basal insulin needs are typically 30–50% of total daily insulin requirement, with the remainder as nutritional coverage using NPH every 12 hours or regular insulin every 6 hours. 3

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Monitoring and Titration After Initiation

• Daily fasting blood glucose monitoring is essential during the titration phase. 2
• Increase basal insulin by 2 units every 3 days if fasting glucose is 140–179 mg/dL. 2
• Increase by 4 units every 3 days if fasting glucose is ≥180 mg/dL. 2
• Target fasting glucose: 80–130 mg/dL. 2
• If hypoglycemia occurs, reduce the dose by 10–20% immediately. 2

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Key Contraindications to Insulin Initiation

• During episodes of hypoglycemia. 5
• Hypersensitivity to insulin glargine or any excipients. 5
• Diabetic ketoacidosis—insulin glargine is not recommended for DKA treatment (use IV regular insulin instead). 5