Diabetes Mellitus

Diagnosis

Classification of diabetes mellitus (DM)

DM can be classified into the following general categories:

1. Type 1 DM: due to autoimmune β-cell destruction, usually leading to absolute insulin deficiency, including latent autoimmune DM of adulthood.
2. Type 2 DM: due to a progressive loss of adequate β-cell insulin secretion, frequently on the background of insulin resistance.
3. Specific types of DM due to other causes, such as monogenic DM syndromes (such as neonatal DM and maturity-onset DM of the young), diseases of the exocrine pancreas (such as cystic fibrosis and pancreatitis), and drug- or chemical-induced DM (such as with glucocorticoid use, in the treatment of human immunodeficiency virus [HIV]/ Acquired Immunodeficiency Syndrome [AIDS], or after organ transplantation).
4. Gestational DM mellitus: DM diagnosed in the second or third trimester of pregnancy that was not clearly overt DM prior to gestation.

Screening criteria for DM

Since patients with DM may not always have symptoms, it is important to recognize those in risk to screen for DM. Criteria for testing for DM in adults are as the following:

1. Testing should be considered in adults with overweight or obesity (body mass index [BMI] ≥ 25 kg/m² or ≥ 23 kg/m² in Asian Americans) who have one or more of the following risk factors:
   • First-degree relative with DM
   • High-risk race/ethnicity (e.g., African American, Latino, Native American, Asian American, Pacific Islander)
   • History of cardiovascular diseases
   • Hypertension (≥140/90 mmHg or on therapy for hypertension)
   • HDL cholesterol level < 35 mg/dL and/or a triglyceride level > 250 mg/dL
   • Women with polycystic ovary syndrome
   • Physical inactivity
   • Other clinical conditions associated with insulin resistance (e.g., severe obesity, acanthosis nigricans)
2. Patients with prediabetes (glycated hemoglobin [HbA1c] ≥ 5.7%, impaired glucose tolerance, or impaired fasting glucose) should be tested yearly.
3. Women who were diagnosed with gestation DM mellitus should have lifelong testing at least every 3 years.
4. For all other patients, testing should begin at age 45 years.
5. If results are normal, testing should be repeated at a minimum of 3-year intervals, with consideration of more frequent testing depending on initial results and risk status.
6. HIV.

Diagnostic criteria for DM

Diagnosis of DM requires two abnormal test results, either from the same sample or in two separate test samples. The diagnostic criteria for DM are:

• Fasting plasma glucose ≥ 126 mg/dL. Fasting is defined as no caloric intake for at least 8 hours.
• OR
• 2-hour plasma glucose ≥ 200 mg/dL during oral glucose tolerance test. The test should be performed as described by World Health Organization (WHO), using a glucose load containing the equivalent of 75 grams of anhydrous glucose dissolved in water.
• OR
• HbA1c ≥ 6.5%. The test should be performed in a laboratory using a method that is NGSP certified (www.ngsp.org) and standardized to the Diabetes Control and Complications Trial (DCCT) reference assay.
• OR
• In a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose ≥ 200 mg/dL.