Glucose Intolerance

Description

• Glucose intolerance is an intermediate stage between a normal glucose metabolism and diabetes. It occurs due to a gradual decline in β-cell function.
• Individuals with impaired fasting glucose (IFG) and/or impaired glucose intolerance (IGT) have been referred to as having prediabetes:
  • IFG: 100 to 125 mg/dL
  • IGT: 140 to 199 mg/dL 2 hours after ingestion of 75 g oral glucose load
  • Hemoglobin A1c (HbA1c) 5.7–6.4% (1)

Epidemiology

• As of 2010, it is estimated that one of every three U.S. adults ≥20 years of age have prediabetes (2).
• In the United States, an estimated 88 million people aged ≥18 years are living with prediabetes as of 2020, based on The National Diabetes Statistics Report.
• Only 11% of people with prediabetes are aware of their condition (3).
• Prediabetes has a 34.5% prevalence among adults >18 years old and 51% of adults ≥65 years old in the United States (4).

Incidence

• Systematic review indicates a 5-year cumulative incidence of developing diabetes of 9–25% for people with an HbA1c of 5.5–6% and 25–50% for people with an HbA1c of 6–6.5% (1).
• Highest incidence in American Indians/Alaska Natives, non-Hispanic blacks, and Hispanics (2)

Prevalence
As of 2020, prevalence of prediabetes in the United States was 34.5% in adults >20 years old and 51% in adults >65 years old. According to ADA, in 2015, 84.1 million Americans >18 years old had prediabetes. As of 2010, worldwide prevalence was 8%.

Etiology and Pathophysiology

Progressive loss of insulin secretion on the background of insulin resistance (1)

Genetics

• Genetic heterogeneity is established by family, twin, immunologic, and HLA disease association studies.
• Variants in 11 genes have been shown to be significantly associated with future development of type 2 diabetes and IFG. Variants in 8 of these genes have been associated with impaired β-cell function.

Risk Factors

• Body mass index (BMI) ≥25: overweight
• History of gestational diabetes mellitus (GDM)
• Sedentary lifestyle
• Medications

General Prevention

• Lifestyle modification with weight reduction and increased physical activity
• A decrease in excess body fat provides the greatest risk reduction.

Pregnancy Considerations

• Screening for diabetes in pregnancy is based on risk factor analysis:
  • High risk: first prenatal visit
  • Average risk: 24 to 28 weeks’ gestation
• Women with GDM should be screened for diabetes 6 to 12 weeks’ postpartum with 75-g OGTT and then every 1 to 3 years via any method (5).

Commonly Associated Conditions

• Obesity (abdominal and visceral obesity)
• Dyslipidemia with high triglycerides (TG)
• PCOS
• GDM
• Congenital diseases (Down, Turner, Klinefelter, and Wolfram syndromes)