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Chapter 223: Type 1 Diabetes Mellitus

Nikhil Goyal; Adam Schlichting

INTRODUCTION AND EPIDEMIOLOGY

Diabetes can be classified into type 1 diabetes (T1DM), type 2 diabetes (T2DM), gestational diabetes, and other specific types of diabetes based on the etiology (Table 223-1); however, many people with diabetes do not easily fit into a single class.1 About 5% of people with diabetes are estimated to have T1DM, which is about 1.25 million American children and adults.2,3

TABLE 223-1Etiologic Classification of Diabetes Mellitus
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TABLE 223-1 Etiologic Classification of Diabetes Mellitus

Type 1 diabetes (β-cell destruction, usually leading to absolute insulin deficiency)

  • Immune mediated

  • Idiopathic

Type 2 diabetes (may range from predominantly insulin resistance with relative insulin deficiency to a predominantly secretory defect with insulin resistance)

Other specific types, such as

  • Genetic defects of β-cell function

  • Genetic defects in insulin action

  • Diseases of the exocrine pancreas (pancreatitis, trauma, cystic fibrosis, etc.)

  • Endocrinopathies (Cushing’s syndrome, pheochromocytoma, hyperthyroidism, somatostatinoma, glucagonoma, etc.)

  • Drug- or chemical-induced (interferon-α, β-adrenergic agonists, diazoxide, phenytoin, glucocorticoids, nicotinic acid, pentamidine, thiazides, thyroid hormone, pyrinuron, etc.)

  • Infections (congenital rubella, cytomegalovirus, etc.)

  • Uncommon forms of immune-mediated diabetes (anti-insulin receptor antibodies in conditions like lupus, etc.)

  • Other genetic syndromes sometimes associated with diabetes (Down’s syndrome, Klinefelter’s syndrome, Turner’s syndrome, etc.)

Gestational diabetes mellitus

PATHOPHYSIOLOGY

T1DM is characterized by an autoimmune, cellular-mediated destruction of β cells of the pancreas. These patients usually have almost no circulating insulin.1 It is mostly diagnosed in children and young adults, but it can also develop in adults.4 Spontaneous ketoacidosis almost always develops in untreated cases, and insulin is required for survival.

Chapter 224, “Type 2 Diabetes Mellitus,” discusses T2DM in detail. Hyperglycemia is present in all types of diabetes mellitus and is the main factor responsible for chronic complications. Therefore, maintaining euglycemic control is the cornerstone of management.

DIAGNOSIS

The American Diabetes Association criteria for diagnosis are listed in Table 223-2.1 Any one of these can be used to make the diagnosis. Patients with a fasting plasma glucose of 100 to 125 milligrams/dL (5.6 to 7.0 mmol/L), a hemoglobin A1C of 5.7% to 6.4%, or a 2-hour plasma glucose of 140 to 199 milligrams/dL (7.8 to 11.0 mmol/L) as part of an oral glucose tolerance test are classified as having prediabetes.4 This should be viewed as an increased risk for diabetes and cardiovascular disease rather than a clinical diagnosis.

TABLE 223-2American Diabetes Association Criteria for the Diagnosis of Diabetes
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TABLE 223-2 American Diabetes Association Criteria for the Diagnosis of Diabetes
A1C ≥6.5%* The test should be performed in a laboratory using a method that is NGSP certified and standardized to the DCCT assay.
Or
Fasting plasma glucose ≥126 milligrams/dL (7.0 mmol/L)* Fasting is defined as no ...

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