Pinning down a type 2 (or prediabetes) diagnosis
The ADA, American Association of Clinical Endocrinologists (AACE), USPSTF, and World Health Organization/International Diabetes Federation agree on the diagnostic criteria for type 2 diabetes: a fasting glucose >126 mg/dL, a random plasma glucose ≥200 mg/dL (that must be confirmed on a subsequent day), or both.5,7,12,13 Patient history, risk factors, and additional laboratory tests can help clinicians distinguish between type 1 and type 2 diabetes.
An oral glucose tolerance test (OGTT) is also an option for diagnosis, but time and scheduling difficulties limit the routine use of this test in primary care. Hemoglobin A1c is not recommended as a diagnostic test because of a lack of standardization.1
Prediabetes and type 2 risk. One in 4 (25.9%) US adults 20 years of age or older and more than 1 in 3 (35.9%) of those 60 years of age or older have prediabetes,14 defined as impaired fasting glucose (100-125 mg/dL), impaired glucose tolerance (2-hour glucose test results of 140-199 mg/dL), or both. Prediabetes increases the risk of developing type 2 diabetes by an estimated 30% over a 4-year period,15 and 70% over 30 years,16 although lifestyle interventions can substantially lower the risk. In a recently released consensus statement, an AACE task force noted that in addition to the increased risk of type 2 diabetes, patients with prediabetes face a greater risk of macrovascular complications.17
Type 2 in kids can be mistaken for type 1
As childhood obesity has surged, type 2 diabetes has been diagnosed at an increasingly early age—even in children younger than 10 years.18 Minority youth, primarily African Americans, Hispanics, and Asians/Pacific Islanders, are at increased risk.14 Symptoms can be insidious in children and adolescents and easily missed or mistaken for type 1 diabetes, in part because type 2 diabetes is still relatively rare in this age group.19
Preteens at risk. In a recent study of BMI and metabolic syndrome risk factors in 8- to 14-year-olds, however, researchers concluded that children who are overweight in early adolescence may be at risk for type 2 diabetes as well as cardiovascular disease before they reach their teens.20 There is evidence of a genetic predisposition for type 2 diabetes and defects of β-cell function,5,21 and family history, in addition to weight, is an important consideration in identifying type 2 diabetes in young patients.
Although young adults with type 1 and type 2 diabetes can present with similar symptoms, there may be certain clues to a type 2 diagnosis. Acanthosis nigricans, which is related to insulin resistance and occurs most frequently in obese adolescents, points to a type 2 diagnosis. Increased insulin and C-peptide levels are indicators of type 2 diabetes. Low levels are not necessarily an indication of type 1, however, because patients with type 2 diabetes may have low levels of insulin and C-peptide because of glucose toxicity and lipotoxicity at the time of diagnosis.22 Treatment with insulin may be necessary until glucose toxicity resolves.
Type 1 diabetes: Beyond childhood
Approximately 5% to 10% of patients with diabetes have type 1, which is defined as idiopathic or cellular immune-mediated autoimmune β-cell destruction.5 The rate of destruction is variable—it generally progresses more rapidly in infants and children than in adults. Some people with type 1 diabetes retain residual β-cell function, but have little or no insulin secretion; this manifests as a low or undetectable level of serum C-peptide.
Most cases of type 1 diabetes are diagnosed in patients younger than 18 years. But type 1 diabetes is increasingly recognized as a disorder that also develops in early adulthood, usually before the age of 40.