Residency · Residency · Medicine Pediatrics

Diabetes Mellitus: Type 1 and Type 2 Across Age Groups

Overview

Type 1 and type 2 diabetes mellitus present distinct challenges across the lifespan. Youth-onset T2DM behaves more aggressively than adult-onset T2DM, with faster beta-cell decline and higher rates of complications. Technology (insulin pumps, continuous glucose monitors) has transformed T1DM management across all ages. The Med-Peds physician must navigate the evolving pharmacotherapy landscape and the unique psychosocial challenges of diabetes in adolescents and young adults.

Type 1 Diabetes Mellitus

Epidemiology and Pathophysiology

Autoimmune destruction of pancreatic beta cells mediated by T lymphocytes. Peak incidence: bimodal (4-6 years and 10-14 years); can present at any age. Increasing incidence worldwide (3-4% annually) Autoantibodies: GAD65 (most common in adults), IA-2, ZnT8, IAA (insulin autoantibodies, most common in young children) Staging (TrialNet): Stage 1: >=2 autoantibodies, normoglycemia, presymptomatic. Stage 2: >=2 autoantibodies, dysglycemia (impaired fasting glucose or glucose tolerance) Stage 3: clinical diabetes (hyperglycemia with symptoms) Teplizumab: anti-CD3 monoclonal antibody; FDA-approved (2022) to delay onset of Stage 3 T1DM in Stage 2 patients >=8 years; delays clinical diabetes by median 2-3 years.

Presentation

Pediatric: polyuria, polydipsia, weight loss, fatigue; DKA at presentation in 30-40% (higher in younger children and delayed diagnosis) Adult-onset T1DM (LADA): latent autoimmune diabetes in adults; slower onset; may initially be misdiagnosed as T2DM; positive autoantibodies (especially GAD65); eventually insulin-dependent. Distinguish from T2DM: younger age, lean habitus, rapid progression to insulin dependence, positive autoantibodies, absence of metabolic syndrome features.

Management: Insulin Therapy

Insulin Regimens

Basal-bolus (MDI): long-acting basal (glargine, detemir, degludec) + rapid-acting bolus with meals (lispro, aspart, glulisine, ultra-rapid lispro/aspart) Insulin pump therapy (CSII): continuous subcutaneous infusion of rapid-acting insulin; basal rate + bolus dosing; allows fine-tuned delivery; preferred in many pediatric programs. Automated insulin delivery (AID) / hybrid closed-loop systems: CGM-integrated pump systems that auto-adjust basal insulin based on sensor glucose. Examples: Medtronic 780G, Tandem Control-IQ, Omnipod 5, Beta Bionics iLet. Significantly improve time-in-range (TIR) and HbA1c while reducing hypoglycemia. Approved for ages 2+ (some systems) to adults.

Glycemic Targets

HbA1c: <7.0% for most children, adolescents, and adults (ADA/ISPAD) Some guidelines suggest <6.5% if achievable without significant hypoglycemia. Time-in-range (TIR): >70% of time with glucose 70-180 mg/dL (CGM-based target) Time below range: <4% (<70 mg/dL), <1% (<54 mg/dL) Individualize targets based on hypoglycemia awareness, age, comorbidities.

Continuous Glucose Monitoring (CGM)

Recommended for ALL patients with T1DM (regardless of insulin delivery method) Options: Dexcom G7, Libre 2/3, Medtronic Guardian 4. Benefits: reduced HbA1c, reduced hypoglycemia, reduced DKA, improved quality of life. Ambulatory glucose profile (AGP): standardized reporting; glucose management indicator (GMI), coefficient of variation (CV <36% indicates stable glycemia)

Acute Complications

Diabetic Ketoacidosis (DKA)

Most common acute complication of T1DM; mortality <1% in developed countries but can be higher in young children (cerebral edema risk) Detailed DKA management covered in Topic 49.

Hypoglycemia

Level 1: 54-70 mg/dL (alert value; self-treat with fast-acting carbohydrate) Level 2: <54 mg/dL (clinically significant; impaired cognition) Level 3: severe hypoglycemia requiring assistance; seizure or loss of consciousness. Treatment: glucose tablets, juice (15 g carb rule); glucagon (IM, SC, or nasal) for severe hypoglycemia. Prevention: CGM alarms, AID systems, hypoglycemia awareness training.

Chronic Complications Screening

Retinopathy: annual dilated eye exam starting at age 11 or 3-5 years after diagnosis (whichever is later) in children; annually in adults. Nephropathy: annual urine albumin/creatinine ratio starting at age 10 or 5 years after diagnosis in children; annually in adults. Neuropathy: annual foot exam starting at puberty or 5 years after diagnosis in children; annually in adults. Cardiovascular risk: lipid panel, BP monitoring; statin therapy in adults with ASCVD risk factors. Thyroid and celiac screening (autoimmune comorbidities): at diagnosis and periodically in children with T1DM.

Type 2 Diabetes Mellitus

Youth-Onset T2DM: A Different Disease

Incidence rising dramatically, paralleling childhood obesity epidemic. Disproportionately affects Black, Hispanic, Native American, and Asian/Pacific Islander youth. Youth-onset T2DM is MORE aggressive than adult-onset: Faster beta-cell decline (TODAY trial: 20-35% failure rate of metformin monotherapy by 5 years) Higher rates of complications at a younger age. More rapid progression to insulin requirement. Higher cardiovascular risk.

Diagnosis (ADA Criteria, Same Across Ages)

Fasting glucose >=126 mg/dL. 2-hour glucose >=200 mg/dL on OGTT. HbA1c >=6.5%. Random glucose >=200 mg/dL with symptoms. In adolescents, distinguish T1DM from T2DM: check C-peptide (preserved/elevated in T2DM, low in T1DM), autoantibodies, clinical features (obesity, acanthosis nigricans, PCOS, family history of T2DM) Up to 10-20% of youth with apparent T2DM have positive autoantibodies ("double diabetes" or autoimmune overlap)

Management of Youth-Onset T2DM

Lifestyle Modification

Nutrition counseling, caloric goals, reduction of sugar-sweetened beverages. Physical activity: >=60 minutes/day of moderate-to-vigorous activity. Behavioral counseling: motivational interviewing, family-based approaches. Weight management: 7-10% weight loss significantly improves glycemic control.

Pharmacotherapy

Metformin: first-line; 500 mg daily titrated to 1000 mg BID (max 2000 mg/day); GI side effects minimized with extended-release formulation. TODAY trial showed high monotherapy failure rate (50% by 5 years) B12 monitoring recommended with long-term use. Insulin: required at diagnosis if HbA1c >=8.5% or DKA; basal insulin added to metformin if targets not met. GLP-1 receptor agonists: liraglutide (approved >=10 years for T2DM), semaglutide (approved >=12 years for obesity); exenatide (approved >=10 years) Ellipse trial: liraglutide + metformin improved HbA1c vs. placebo in youth. Increasingly used as second-line after metformin. SGLT2 inhibitors: empagliflozin (approved >=10 years for T2DM); dapagliflozin (under study in youth) Other: sulfonylureas, thiazolidinediones, DPP-4 inhibitors (limited pediatric data)

Management of Adult T2DM

Pharmacotherapy Advances

Metformin: remains first-line for most adults. SGLT2 inhibitors: cardiorenal benefit independent of glycemic control (EMPA-REG, CREDENCE, DAPA-CKD); standard of care if ASCVD, HF, or CKD. GLP-1 receptor agonists: cardiovascular benefit (LEADER, SUSTAIN-6, SELECT trials); weight loss; semaglutide (oral and injectable), liraglutide, dulaglutide, tirzepatide (dual GIP/GLP-1 agonist with superior HbA1c and weight reduction) Insulin: still needed for many; basal insulin preferred initially; intensify as needed. Combination approach: early combination therapy increasingly recommended to achieve durable glycemic control.

ADA 2024 Glycemic Targets (Adults)

HbA1c <7.0% for most non-pregnant adults. More stringent (<6.5%) if achievable without hypoglycemia. Less stringent (<8.0%) for patients with limited life expectancy, extensive comorbidities, or hypoglycemia unawareness.

Screening for T2DM

Pediatric Screening (ADA)

Screen overweight/obese youth (BMI >=85th percentile) with >=1 additional risk factor: Family history of T2DM in 1st or 2nd degree relative; High-risk race/ethnicity; Signs of insulin resistance (acanthosis nigricans, PCOS, dyslipidemia, HTN); Maternal history of GDM; Begin screening at age 10 or onset of puberty (whichever is earlier); Repeat every 3 years (or more frequently if BMI increasing or risk factors accumulate).

Adult Screening (ADA)

All adults starting at age 35 (or earlier if overweight/obese + risk factors) Screen every 3 years if normal results. Annual screening for prediabetes.

Special Populations

Diabetes in Pregnancy

Pre-gestational T1DM and T2DM: optimize HbA1c <6.5% before conception; switch to insulin if on oral agents; tight glucose monitoring; high-risk obstetric care. Gestational diabetes: screen at 24-28 weeks; lifestyle modification first; insulin if targets not met; metformin considered second-line. Postpartum: screen for persistent diabetes at 4-12 weeks postpartum; lifelong screening every 1-3 years.

Monogenic Diabetes (MODY)

1-5% of all diabetes; autosomal dominant; often misdiagnosed as T1DM or T2DM. Suspect if: strong family history of diabetes across >=3 generations, onset <25 years, negative autoantibodies, preserved C-peptide, non-obese. Common subtypes: GCK-MODY (MODY2, mild fasting hyperglycemia, usually no treatment needed), HNF1A-MODY (MODY3, sulfonylurea-responsive), HNF4A-MODY (MODY1) Genetic testing confirms diagnosis; dramatically changes management (sulfonylureas instead of insulin for HNF1A/HNF4A-MODY)

<image>A comprehensive comparison diagram of T1DM and T2DM across age groups. Four quadrants show: (1) Pediatric T1DM -- autoimmune pathophysiology with beta-cell destruction, insulin-dependent from onset, technology-centric management with AID systems; (2) Adult T1DM/LADA -- slower onset, positive autoantibodies, may initially mimic T2DM; (3) Youth-onset T2DM -- aggressive course, fast beta-cell decline, TODAY trial failure rates; (4) Adult T2DM -- insulin resistance predominant, multiple pharmacotherapy options, cardiovascular risk management. Each quadrant shows key features, treatment approach, and glycemic targets.</image>

<image>A pharmacotherapy algorithm for youth-onset T2DM versus adult T2DM. The youth panel shows metformin as first-line, with branching to insulin (if HbA1c above 8.5% or DKA), GLP-1 RA (liraglutide, semaglutide), and SGLT2i (empagliflozin) with their FDA-approved pediatric ages. The adult panel shows metformin first-line with the ADA cardiorenal-guided algorithm: if ASCVD/high risk, add GLP-1 RA or SGLT2i; if HF or CKD, add SGLT2i; if additional glycemic control needed, add insulin or other agents. The connecting theme emphasizes that youth-onset T2DM is more aggressive and is increasingly being treated with agents borrowed from the adult toolkit.</image>

<image>A diabetes technology overview showing the evolution of glucose monitoring and insulin delivery. From left to right: fingerstick glucose monitoring (traditional), CGM devices (Dexcom, Libre) showing real-time glucose tracings with time-in-range highlighted, insulin pens (MDI regimen), insulin pumps (patch and tubed), and automated insulin delivery systems (hybrid closed-loop with CGM-pump communication). An ambulatory glucose profile report is shown demonstrating the key metrics: TIR above 70%, time below range less than 4%, GMI, and CV. Age ranges for device approval are annotated.</image>

Clinical Pearls

Youth-onset T2DM is a MORE aggressive disease than adult-onset T2DM -- faster beta-cell decline, higher complication rates, and poorer response to metformin monotherapy. Teplizumab (anti-CD3) is the first FDA-approved therapy to delay onset of clinical T1DM in high-risk individuals (Stage 2) -- a breakthrough in disease modification. CGM should be offered to ALL patients with T1DM regardless of age or insulin delivery method -- it reduces HbA1c, hypoglycemia, and DKA. Time-in-range (TIR >70%) is increasingly used alongside HbA1c as a glycemic management target. Always check autoantibodies and C-peptide in adolescents with new diabetes to distinguish T1DM from T2DM -- up to 10-20% of apparent T2DM have autoimmune overlap. Consider MODY in young, non-obese patients with strong family history of diabetes, negative autoantibodies, and preserved C-peptide -- genetic testing changes management dramatically. SGLT2 inhibitors and GLP-1 agonists have transformed adult T2DM management with cardiorenal benefits beyond glycemic control -- their role in youth-onset T2DM is expanding. DKA can be the presenting diagnosis of BOTH T1DM and T2DM in youth -- do not assume DKA means T1DM.

References

• ElSayed NA, Aleppo G, Aroda VR, et al. Standards of Care in Diabetes -- 2024 (ADA). Diabetes Care. 2024;47(Suppl 1):S1-S321.
• Zeitler P, Hirst K, Pyle L, et al. A clinical trial to maintain glycemic control in youth with type 2 diabetes (TODAY trial). N Engl J Med. 2012;366(24):2247-2256.
• Herold KC, Bundy BN, Long SA, et al. An anti-CD3 antibody, teplizumab, in relatives at risk for type 1 diabetes (TrialNet). N Engl J Med. 2019;381(7):603-613.
• Brown SA, Kovatchev BP, Raghinaru D, et al. Six-month randomized, multicenter trial of closed-loop control in type 1 diabetes (iDCL trial). N Engl J Med. 2019;381(18):1707-1717.
• Drucker DJ. The GLP-1 journey: from discovery science to therapeutic impact. J Clin Invest. 2024;134(2):e175634.

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