What is the recommended initial insulin regimen and additional blood tests for an 18-year-old patient with newly diagnosed type 1 diabetes mellitus (T1DM)?

Initial Insulin Regimen for 18-Year-Old with Newly Diagnosed Type 1 Diabetes

Start with a basal-bolus regimen using 0.5 units/kg/day total daily dose, split 50% as long-acting basal insulin (glargine or detemir) once daily and 50% as rapid-acting insulin (lispro, aspart, or glulisine) divided among three meals. 1, 2

Calculating the Initial Insulin Dose

• For metabolically stable patients with type 1 diabetes, begin with 0.5 units/kg/day as the total daily insulin dose (TDD). 1, 2, 3
• If the patient presents with diabetic ketoacidosis or severe hyperglycemia, use higher weight-based dosing immediately. 1, 2
• The acceptable range for TDD is 0.4-1.0 units/kg/day, but 0.5 units/kg/day is the standard starting point for most newly diagnosed patients. 1, 3

Distribution Between Basal and Prandial Insulin

• Give 40-50% of the TDD as basal insulin (long-acting analog like glargine or detemir) administered once daily at the same time each day. 1, 3
• Administer the remaining 50-60% as prandial insulin (rapid-acting analog like lispro, aspart, or glulisine) divided among three meals. 1, 3
• Rapid-acting insulin should be given 0-15 minutes before meals, not after eating. 4, 5

Specific Insulin Formulations for Adolescents

• Insulin glargine and glulisine can be used in children above 6 years of age. 5
• Insulin lispro can be used in children above 3 years of age. 5
• Insulin detemir and aspart can be used in children above 2 years of age. 5
• All rapid-acting analogs (aspart, glulisine, lispro) are preferred over regular human insulin for better postprandial glucose control. 6, 3

Glycemic Targets for This Age Group

• The target HbA1c for an 18-year-old with type 1 diabetes is <7.5%. 3, 5
• Pre-meal self-monitored blood glucose should be 90-130 mg/dL (or 80-130 mg/dL per some guidelines). 5, 3
• Bedtime blood glucose should be 100-140 mg/dL. 5

Dose Titration Strategy

• Adjust basal insulin based on fasting glucose patterns, increasing by 2 units every 3 days if fasting glucose is 140-179 mg/dL, or by 4 units every 3 days if fasting glucose is ≥180 mg/dL. 2, 3
• Adjust prandial insulin by 1-2 units or 10-15% every 3 days based on postprandial glucose readings. 2
• If hypoglycemia occurs, reduce the relevant insulin dose by 10-20% immediately. 2, 3

Essential Patient Education Components

• Teach carbohydrate counting and insulin-to-carbohydrate ratios (typically starting at 1:10 to 1:15 for adolescents). 2, 3
• Educate on recognition and treatment of hypoglycemia using 15 grams of fast-acting carbohydrate when blood glucose is ≤70 mg/dL. 2
• Provide instruction on proper insulin injection technique, site rotation, and avoiding lipohypertrophy. 4, 3
• Teach "sick day" management rules, including assessment for ketosis with every illness. 3, 2

Technology Integration

• Integrate continuous glucose monitoring (CGM) into the treatment plan soon after diagnosis, as it improves glycemic outcomes, decreases hypoglycemic events, and improves quality of life. 3
• Consider automated insulin delivery (AID) systems or insulin pump therapy for patients requiring more flexibility or not meeting targets with multiple daily injections. 3, 7

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Additional Blood Tests for Screening Other Conditions in Type 1 Diabetes

At diagnosis of type 1 diabetes, screen for celiac disease with tissue transglutaminase antibodies (tTG-IgA) and total IgA, and screen for thyroid dysfunction with TSH and thyroid peroxidase antibodies (TPO). 3

Autoimmune Screening at Diagnosis

• Screen for celiac disease at diagnosis using tissue transglutaminase antibodies (tTG-IgA) with total IgA level. 3
• Screen for thyroid autoimmunity with TSH and thyroid peroxidase antibodies (TPO) at diagnosis. 3
• These autoimmune conditions are more common in patients with type 1 diabetes and require early detection. 3

Baseline Metabolic Assessment

• Obtain baseline HbA1c, fasting lipid profile (total cholesterol, LDL, HDL, triglycerides), and comprehensive metabolic panel including kidney function (creatinine, eGFR). 3
• Check urine albumin-to-creatinine ratio to establish baseline kidney function. 3
• Baseline vitamin D level may be considered, though evidence for routine supplementation is limited. 3

Ongoing Screening Schedule

• Rescreen for celiac disease every 1-2 years if initial screening is negative, especially if gastrointestinal symptoms develop. 3
• Rescreen thyroid function (TSH) annually or if symptoms of thyroid dysfunction appear. 3
• Screen for diabetic retinopathy starting at age 11 years with diabetes duration of 2-5 years, then annually thereafter. 3
• Screen for diabetic nephropathy annually starting at age 11 years with diabetes duration of 5 years. 3

Common Pitfalls to Avoid

• Do not delay insulin initiation or use inadequate doses—type 1 diabetes requires immediate full insulin replacement. 4, 5
• Do not use premixed insulins as initial therapy in type 1 diabetes, as they lack the flexibility needed for optimal control. 4, 3
• Do not forget to screen for associated autoimmune conditions, as they are frequently present and require separate management. 3
• Avoid injecting into areas of lipohypertrophy, as this distorts insulin absorption and worsens glycemic control. 4