Type 1 and type 2 diabetes

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"type 1 diabetes" OR "type 2 diabetes" management

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Type 1 and Type 2 Diabetes Mellitus

Overview

Diabetes mellitus (DM) is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. Approximately 34 million Americans (10.5% of the U.S. population) have diabetes. Type 2 accounts for about 90% of all cases; type 1 makes up most of the remainder. - Mulholland & Greenfield's Surgery, 7e

Key Comparison at a Glance

Feature	Type 1 DM	Type 2 DM
Mechanism	Autoimmune beta-cell destruction	Insulin resistance + progressive beta-cell dysfunction
Body habitus	Usually lean	Usually overweight/obese
Onset	Typically childhood/adolescence (mean: early teens)	Typically >40, but rising in youth
Ketosis	Prone to DKA	Prone to hyperosmolar hyperglycemic state (HHS)
Insulin dependency	Always required	Often not initially required
Autoantibodies	Present (anti-GAD, anti-IA2, etc.)	Absent
HLA association	Strong (HLA-DR3, DR4)	Weak
Insulin levels	Very low/absent	Normal, elevated, or reduced

Type 1 Diabetes

Pathophysiology

Type 1 DM results from a chronic autoimmune process - usually present in a preclinical state for years before clinical onset. The hallmarks are destruction of pancreatic islet beta-cells, with near-total absence of insulin-secreting cells while glucagon-secreting alpha cells, somatostatin-secreting delta cells, and pancreatic polypeptide cells are preserved. Proinsulin is the most likely primary autoimmune target. - Rosen's Emergency Medicine, 10e

The underlying cause is multigenic - genes within the HLA region (especially antigen-presenting molecules) confer the greatest genetic risk. Monozygotic twin concordance is less than 100%, confirming the role of environmental triggers (possibly viral) in initiating autoimmunity and insulitis. - Mulholland & Greenfield's Surgery, 7e

Three recognizable stages (Tietz Lab Medicine, 7e):

Stage 1: Normoglycemia + multiple islet autoantibodies
Stage 2: Dysglycemia (impaired fasting glucose/impaired glucose tolerance) + autoantibodies
Stage 3: Clinical hyperglycemia with symptoms

If two or more autoantibodies are present, risk of progression to clinical T1DM is 75% over 10 years and near-certain over a lifetime. - Mulholland & Greenfield's Surgery, 7e

Clinical Features

Classic triad: polyuria, polydipsia, polyphagia
Typically presents in lean patients
Peak incidence in childhood and adolescence (75% before age 18), but can present at any age
A short "honeymoon period" may follow initial diagnosis where minimal exogenous insulin is needed - this does not last
Exogenous insulin is always required to sustain life and prevent ketosis

Type 2 Diabetes

Pathophysiology

The classic picture is peripheral insulin resistance combined with progressive beta-cell dysfunction. Insulin levels may be normal, elevated, or decreased - the key issue is impaired insulin action in target tissues (liver, muscle, adipose). - Tietz Textbook of Laboratory Medicine, 7e

The pathogenesis involves:

Insulin resistance in skeletal muscle and liver (often decades in development)
Compensatory hyperinsulinemia initially maintains euglycemia
Progressive beta-cell exhaustion - beta-cells can no longer compensate for the resistance
Relative insulinopenia and frank hyperglycemia result

Obesity drives insulin resistance, and weight loss alone can substantially improve glycemic control in many patients.

Clinical Features

Minimal symptoms at onset; often discovered incidentally on screening
Not prone to ketosis under normal circumstances (sufficient residual insulin to block unrestrained lipolysis)
Extremely high glucose can cause hyperosmolar hyperglycemic state (HHS) - a medical emergency where severe dehydration and hyperosmolality dominate without significant ketoacidosis
Many patients can initially be managed with lifestyle modification and oral agents, but many eventually require insulin

Diagnosis (ADA Criteria)

Any ONE of the following confirms diabetes (requires repeat confirmation in asymptomatic individuals):

Test	Diabetes	Prediabetes
Fasting plasma glucose (FPG)	≥126 mg/dL (7.0 mmol/L)	100-125 mg/dL
2-hour OGTT	≥200 mg/dL (11.1 mmol/L)	140-199 mg/dL
HbA1c	≥6.5%	5.7-6.4%
Random glucose + symptoms	≥200 mg/dL	-

A markedly elevated random glucose (>200 mg/dL) with classic symptoms does not require confirmation. - Harrison's Principles of Internal Medicine 22e (2025)

Note: HbA1c may be unreliable in hemoglobinopathies and certain ancestries - clinical judgment is needed.

Complications

Both types share the same spectrum of complications, driven by chronic hyperglycemia through nonenzymatic glycation of proteins and oxidative stress. - Basic Medical Biochemistry, 6e

Microvascular (small vessel disease):

Retinopathy - leading cause of blindness in working-age adults
Nephropathy - leading cause of end-stage renal disease
Neuropathy - peripheral and autonomic

Macrovascular (large vessel disease):

Coronary artery disease
Cerebrovascular disease (stroke)
Peripheral arterial disease

Cardiovascular disease is the most prevalent cause of mortality and morbidity in diabetic patients. - Fuster and Hurst's The Heart, 15e

Management

Type 1 DM

Insulin therapy is always required (multiple daily injections or continuous subcutaneous infusion via pump)
Basal-bolus regimens mimic physiologic insulin secretion
Continuous glucose monitoring (CGM) is now standard of care
Target HbA1c: generally <7% (individualized)

Type 2 DM

Management is stepwise, typically:

Lifestyle modification - diet, exercise, weight loss (cornerstone)
Metformin - first-line pharmacotherapy; reduces hepatic gluconeogenesis; does not cause weight gain or hypoglycemia; avoid if GFR <30 mL/min/1.73m²
Add-on agents as needed (HbA1c target <7%):

Drug Class	Examples	Key Feature
Sulfonylureas	Glipizide, glimepiride	Stimulate insulin release; risk of hypoglycemia
Thiazolidinediones	Pioglitazone, rosiglitazone	Insulin sensitizers; cardiac risk concerns
GLP-1 receptor agonists	Semaglutide, liraglutide	Weight loss, CV benefit
SGLT-2 inhibitors	Empagliflozin, dapagliflozin	Renal/CV protection, weight loss
DPP-4 inhibitors	Sitagliptin	Weight neutral
Alpha-glucosidase inhibitors	Acarbose	Reduce post-meal glucose absorption
Insulin	Multiple formulations	Used when oral agents insufficient

Rosen's Emergency Medicine, 10e

Recent evidence: A 2025 systematic review (PMID 40952752) confirmed efficacy and safety of GLP-1 receptor agonists in children and adolescents with obesity or T2DM, expanding their use in younger populations.

Screening (Type 2 DM)

Screen adults who are overweight/obese (BMI ≥25, or ≥23 in Asian Americans) with any of:

Family history of diabetes
High-risk race/ethnicity (African American, Latino, Native American, Asian American, Pacific Islander)
Hypertension (BP ≥130/80 mmHg)
HDL <35 mg/dL or triglycerides >250 mg/dL
Polycystic ovary syndrome or acanthosis nigricans
History of cardiovascular disease
Harrison's Principles of Internal Medicine 22e

Summary

Type 1 and Type 2 diabetes share the endpoint of hyperglycemia and its complications, but differ fundamentally in mechanism, onset, and management. Type 1 is an autoimmune disease requiring lifelong insulin; Type 2 is primarily a disease of insulin resistance and metabolic dysfunction, where lifestyle and escalating pharmacotherapy are the mainstay. Both demand tight glycemic control (HbA1c <7% in most patients) to prevent the devastating microvascular and macrovascular sequelae that dominate long-term morbidity and mortality.

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