Prediabetes
Prediabetes is defined by plasma glucose levels that are elevated above the normal range, but below the threshold for diabetes. Early diagnosis of prediabetes identifies persons at risk and prevents progression to type 2 diabetes mellitus (T2DM) and cardiovascular disease.
The glucose thresholds for prediabetes have changed over the years; therefore, this article will focus on data from the past decade.
Definitions of Prediabetes
Prediabetes is defined differently by the American Diabetes Association (ADA) and the World Health Organization (WHO).
ADAdefinition of prediabetes. Patients are at increased risk for diabetes if they have 1 of the following 3 states:
• Impaired fasting glucose (IFG): IFG is a fasting plasma glucose level of 100-125 mg/dL. This threshold was introduced by the ADA in 2003; before 2003, the threshold was 110-125 mg/dL. The threshold was lowered to increase sensitivity and identify more patients at risk of developing diabetes. The downside of lowering the threshold is that a higher proportion of the population is classified as potentially having a disease. This may be particularly important in children.
• Impaired glucose tolerance (IGT): A plasma glucose level (obtained 2 hours after a 75-g oral glucose challenge) > 140 mg/dL but < 200 mg/dL.
• Hemoglobin A1c (A1c): Beginning in 2010, the ADA included an A1c level of 5.7%-6.4% as an indicator of prediabetes. The advantage of A1c measurement is that it reflects plasma glucose levels over time and does not require fasting. However, this definition is controversial and has not been well studied in pediatric populations.
WHO definition of prediabetes. Patients are at increased risk for diabetes if they have 1 or both of the 2 following states:
• IFG: a fasting plasma glucose level of 110-125 mg/dL; or
• IGT: a plasma glucose level (obtained 2 hours after a 75-g oral glucose challenge) > 140 mg/dL but < 200 mg/dL.
Neither definition of prediabetes includes other risk factors for diabetes, such as family history of diabetes, obesity, or parameters of the metabolic syndrome.
Many patients with prediabetes will not convert to T2DM. For this reason, the WHO diabetes task force suggested using different terminology, such as "intermediate hyperglycemia." Furthermore, the reproducibility of thresholds used to define prediabetes is low (approximately 50%).