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Diabetes is characterized by hyperglycemia due to defects in insulin action or insulin secretion. There are two types of diabetes: type 1 (T1DM) and type 2 (T2DM). Additional subclasses include gestational diabetes mellitus (GDM) and secondary diabetes associated with hormonal syndromes, medications, and diseases of the pancreas. The key differences between T1DM and T2DM are the pathophysiology, etiology of hyperglycemia, and clinical presentation.

T1DM is a cellular-mediated autoimmune process that destroys pancreatic β-cells resulting in insulin deficiency. Due to the lack of insulin, glucose is not able to be used as energy. The onset of symptoms leading to the diagnosis of T1DM is abrupt and includes polydipsia, polyuria, polyphagia, weight loss, or ketoacidosis. T2DM is impaired insulin secretion and insulin resistance at sites such as the liver, muscles, and adipocytes. Patients with T2DM are able to produce insulin, but the amount may not be sufficient to keep up with the body’s glucose metabolism. Additionally, the insulin that is produced by a patient with T2DM may not work appropriately at its receptor sites.


Pregnant women, overweight adults, and children who are at risk for diabetes should be screened (Table 60-1). Screening identifies patients likely to develop or have diabetes. The American Diabetes Association (ADA) does not recommend fasting glucose levels as a measure of screening every patient. Patients at risk complete the ADA Diabetes Risk Screening Test. If a patient scores a 10 or greater, a finger stick blood sample is recommended. The online version of this screening tool is available at The diagnosis of diabetes or prediabetes is via evaluation of hemoglobin A1c, fasting or random plasma glucose level, or the oral glucose tolerance test (OGTT) (Table 60-2). The hemoglobin A1c evaluates glucose control over the last 2 to 3 months and can be expressed as the estimated average glucose (eAG) level. The eAG is expressed as measures of blood glucose levels. The eAG equation is: eAG (mg/dL) = 28.7 × A1c − 46.7.

TABLE 60-1Screening Recommendations for Diabetes in Adults, Children, and Pregnancy (GDM)

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