Evaluation of De Novo (New-Onset) Type 1 Diabetes

1. Confirm the Diagnosis of Diabetes

2. Islet Autoantibody Panel (Confirm T1DM Etiology)

3. Beta-Cell Reserve: C-Peptide

• Fasting and stimulated C-peptide are used to measure residual beta-cell function
• Low/undetectable C-peptide confirms absolute insulin deficiency of T1DM
• C-peptide is preferred over insulin because it is not affected by exogenous insulin injections
• Glucagon stimulation test or Mixed Meal Tolerance Test (MMTT) can be used to provoke maximal C-peptide response - (Henry's Clinical Diagnosis, p. 619)
• Urine C-peptide:creatinine ratio is also useful in outpatient settings
• Note: C-peptide is elevated in renal failure (degraded renally, unlike insulin)

4. HbA1c

• Reflects 2-3 month average glycemia
• Helps quantify the degree of hyperglycemia at presentation
• Used to monitor therapy going forward (target generally <7% in most adults)

5. Screen for Associated Autoimmune Conditions

6. Genetic Testing (Selected Cases)

• HLA typing (HLA-DQ/DR): HLA-DR4-DQ8 and DR3-DQ2 are present in ~90% of T1DM children. DR15-DQ6 is protective (found in only 1% with T1DM vs. 20% general population). - (Goldman-Cecil, p. 2472)
• Genetic testing is not routine clinical practice but is used in:
  • Distinguishing T1DM from MODY (Maturity-Onset Diabetes of the Young)
  • Research screening of first-degree relatives
  • Counseling regarding recurrence risk in family members

7. Differentiate from Mimics

8. Baseline Complication Screening

9. Acute Assessment at Presentation

• Arterial blood gas / venous blood gas - if DKA suspected (anion gap, pH)
• Serum electrolytes, BMP - Na, K, bicarbonate, BUN, creatinine
• Urine ketones / serum beta-hydroxybutyrate - confirm ketosis/ketoacidosis
• CBC - may show leukocytosis during DKA (stress response)

Summary Checklist for De Novo T1DM

☐ Confirm diagnosis: FPG / OGTT / HbA1c
☐ Islet autoantibodies: GAD65, IA-2, ZnT8, IAA (before insulin started)
☐ C-peptide (fasting ± stimulated): assess residual beta-cell function
☐ HbA1c: degree of glycemic control
☐ Metabolic panel + ketones/pH: rule out DKA
☐ Thyroid function (TSH, anti-TPO): associated autoimmune screen
☐ Celiac serology (anti-tTG IgA + total IgA)
☐ Adrenal screen (morning cortisol) if features of APS-2
☐ Lipid panel, blood pressure: cardiovascular risk
☐ Urine ACR, eGFR: baseline renal function
☐ Ophthalmology referral: baseline retinal screen
☐ MODY genetics if: no autoantibodies + family history + lean young adult + mild fasting hyperglycemia

Treatment of Type 1 Diabetes Mellitus - Evidence-Based Guidelines

Guideline sources: ADA Standards of Care in Diabetes 2025, ADA/EASD Consensus Report on T1DM Management in Adults, Goldman-Cecil Medicine (2024), Katzung's Pharmacology 16e, Textbook of Family Medicine 9e

1. Overarching Goals

2. Insulin Therapy (The Cornerstone)

2a. Insulin Types and Pharmacokinetics

• (Goldman-Cecil Medicine, Table 210-4, p. 2474)

Long-acting analogues (glargine, detemir, degludec) produce less hypoglycemia and less weight gain than NPH, and have more predictable absorption. They are preferred over NPH.

2b. Multiple Daily Injection (MDI) - "Basal-Bolus" Regimen

• Total Daily Dose (TDD): 0.3-1.0 unit/kg/day
• 50% as basal insulin (once or twice daily long-acting analogue)
• 50% divided as prandial boluses before each meal

• 1 unit per 10-15 g carbohydrate consumed (insulin-to-carb ratio, varies by time of day)
• Plus a correction factor: 1 unit lowers blood glucose by ~20-50 mg/dL (individualized)

2c. Continuous Subcutaneous Insulin Infusion (CSII - Insulin Pump)

• Better HbA1c control (reduces HbA1c by ~0.3-0.5%)
• Less hypoglycemia (especially nocturnal)
• Adjustable basal rates for exercise, illness, dawn phenomenon
• Better quality of life scores

• Frequent hypoglycemia or hypoglycemia unawareness
• Dawn phenomenon causing AM hyperglycemia
• Poor glycemic control despite MDI
• Lifestyle flexibility needs (shift workers, athletes)
• Motivated, educated patients willing to self-monitor glucose 4-6x/day

2d. Closed-Loop Systems ("Artificial Pancreas") - Current Best Practice

• CGM continuously measures interstitial glucose
• Algorithm automatically adjusts basal insulin delivery
• Patient still doses bolus insulin at meals (hybrid closed loop)

3. Glucose Monitoring

3a. Continuous Glucose Monitoring (CGM) - Preferred

• Real-time or flash CGM is now recommended for all T1DM patients regardless of treatment mode
• Studies show improved glucose control without increased hypoglycemia with CGM in adults ≥25 years on intensive insulin
• CGM alarms help detect and prevent hypoglycemia
• The CONCEPTT Trial (2017) showed CGM improved outcomes even in pregnant women with T1DM

3b. Self-Monitoring of Blood Glucose (SMBG)

• If CGM not available: monitor at minimum before meals, 2 hours post-meal, at bedtime, before exercise, and when symptomatic
• Test urine or capillary ketones if glucose persistently >250 mg/dL (>2+ = urgent care)

4. Diet and Lifestyle

• Carbohydrate counting is the preferred nutrition approach - allows flexible prandial dosing
• Carbohydrate consistency (fixed grams/meal) is an alternative for simpler dosing
• Learn to read food labels; consider a registered dietitian referral at diagnosis
• No specific carbohydrate target; generally 45-60% of calories for most
• Rapidly-absorbed carbohydrates (high GI foods) should be minimized
• Mediterranean diet recommended for cardiovascular benefit
• Caloric restriction only needed if overweight/obese
• Exercise: Regular aerobic and resistance exercise is recommended. Adjust insulin doses and carbohydrate intake around physical activity. Monitor glucose before, during, and after exercise. A 2025 EASD/ISPAD Position Statement (PMID 39657609) addresses automated insulin delivery around exercise. - (Goldman-Cecil, p. 2475)

5. Adjunctive Pharmacological Therapies

Important: SGLT2 inhibitors are not approved for T1DM in the United States due to DKA risk. They are available in some countries as adjuncts in adults who are overweight. If used, patients must be educated to monitor ketones. - (Goldman-Cecil, p. 2475)

6. Management of Acute Complications

6a. Hypoglycemia ("15-15 Rule")

• Mild/moderate (glucose <70 mg/dL, alert): 15 g fast-acting carbohydrate (4 glucose tablets, 150 mL juice); recheck in 15 min; repeat if still <70 mg/dL
• Severe (unconscious/unable to swallow): IM/SC glucagon (1 mg) OR IV dextrose 25 g (50 mL of 50% dextrose)
• Glucagon options: Traditional 1 mg IM kit; or nasal glucagon (Baqsimi) 3 mg intranasal - no reconstitution needed
• Hypoglycemia unawareness: raise glucose targets temporarily; structured hypoglycemia avoidance programs

6b. Diabetic Ketoacidosis (DKA)

• IV fluid resuscitation: Normal saline 1-2 L/hour initially, then 250-500 mL/hour
• Insulin: IV regular insulin infusion 0.1 unit/kg/hour (or 0.14 unit/kg/hour without bolus)
• Potassium replacement: Add K+ to IV fluids when K+ <5.5 mEq/L and adequate urine output; K+ must be ≥3.5 mEq/L before insulin started
• Bicarbonate: Only if pH <6.9
• Transition to SC insulin: When glucose <200-250 mg/dL, anion gap closed, patient tolerating oral intake - overlap SC and IV insulin by 1-2 hours before stopping drip
• Monitor glucose hourly; electrolytes every 2-4 hours

7. Technology Hierarchy (ADA 2025 Preferred Approach)

BEST: Closed-loop (hybrid/advanced hybrid)
         ↑
      CGM + CSII (open-loop)
         ↑
      CGM + MDI (basal-bolus)
         ↑
      SMBG + MDI (basal-bolus)  ← minimum standard
         ↑
AVOID: Single or twice-daily injections alone

8. Disease-Modifying Therapy (Prevention)

• Teplizumab (Tzield): Anti-CD3 monoclonal antibody, FDA approved (2022) for Stage 2 T1DM (2+ autoantibodies + impaired glucose tolerance in patients ≥8 years). 14-day IV infusion. Delays progression to Stage 3 (clinical) T1DM by ~25 months. - (Katzung 16e, p. 1174)
• Not a treatment for established T1DM - used in pre-symptomatic at-risk individuals

9. Monitoring and Follow-Up

10. Multidisciplinary Team

• Endocrinologist (primary management)
• Certified Diabetes Care and Education Specialist (CDCES)
• Registered Dietitian Nutritionist (RDN)
• Mental health professional
• Ophthalmologist / Podiatrist / Nephrologist as complications develop

Key Recent Guideline Updates (2024-2026)

• ADA Standards of Care 2025: Updated HbA1c targets, CGM as standard of care, closed-loop recommendation strengthened
• EASD/ISPAD Position Statement 2025 (PMID 39657609): Automated insulin delivery around exercise guidance
• International Consensus on CGM in Pregnancy with T1DM (2026, PMID 41421368): CGM + automated insulin delivery recommended during pregnancy
• Continuous Ketone Monitoring Expert Recommendations (2026, PMID 41381175): New technology for DKA prevention guidance