What are the diagnostic criteria for prediabetes in adults?

Diagnostic Criteria for Prediabetes

Prediabetes is diagnosed when any one of three tests shows abnormal glucose metabolism: fasting plasma glucose (FPG) 100-125 mg/dL, 2-hour plasma glucose during 75-g oral glucose tolerance test (OGTT) 140-199 mg/dL, or hemoglobin A1C 5.7-6.4%. 1

Three Equivalent Diagnostic Tests

The most recent American Diabetes Association guidelines (2025) define prediabetes using any of these criteria 1:

• Impaired Fasting Glucose (IFG): FPG 100-125 mg/dL (5.6-6.9 mmol/L)
• Impaired Glucose Tolerance (IGT): 2-hour plasma glucose 140-199 mg/dL (7.8-11.0 mmol/L) during 75-g OGTT
• Elevated A1C: 5.7-6.4% (39-47 mmol/mol)

All three tests are considered equally appropriate for diagnosis 2. You can use whichever is most practical in your clinical setting.

Important Nuances About the Criteria

The IFG Threshold Controversy

A critical caveat: The World Health Organization (WHO) and many international diabetes organizations use a higher IFG cutoff of 110 mg/dL (6.1 mmol/L) rather than the ADA's 100 mg/dL 2. The ADA lowered this threshold in 2003 to equalize diabetes risk between IFG and IGT, but this remains controversial 3. The lower threshold captures more people—approximately half will test normal on repeat testing and one-third spontaneously revert to normal over time 3.

A1C Limitations

When using A1C, recognize several important limitations 2:

• Red blood cell turnover conditions: In sickle cell disease, pregnancy (second/third trimesters), hemodialysis, recent blood loss/transfusion, or erythropoietin therapy, only use plasma glucose criteria—A1C is unreliable
• Hemoglobin variants: Most U.S. assays handle common variants, but marked discrepancies between A1C and glucose should prompt suspicion
• Age considerations: The evidence base for A1C diagnostic criteria comes from adult populations only

OGTT Requirements

If using OGTT as a screening tool, ensure adequate carbohydrate intake of at least 150 g/day for 3 days prior to testing 4.

Who Should Be Tested

Testing should be considered in 1:

1. Adults with overweight/obesity (BMI ≥25 kg/m² or ≥23 kg/m² in Asian Americans) who have ≥1 additional risk factor:

   • First-degree relative with diabetes
   • High-risk race/ethnicity (African American, Latino, Native American, Asian American)
   • History of cardiovascular disease
   • Hypertension (≥130/80 mmHg or on therapy)
   • HDL <35 mg/dL and/or triglycerides >250 mg/dL
   • Polycystic ovary syndrome
   • Physical inactivity
   • Conditions associated with insulin resistance (severe obesity, acanthosis nigricans, metabolic dysfunction-associated steatotic liver disease)

2. All other adults starting at age 35 years (updated from age 45 in earlier guidelines 5)

3. Repeat testing: Every 3 years if normal, but yearly if prediabetes is diagnosed 2, 1

Clinical Significance

Prediabetes represents a high-risk state rather than a disease entity 2. The A1C range of 5.7-6.4% identifies individuals with diabetes risk similar to high-risk Diabetes Prevention Program participants 2. Those with A1C 6.0-6.5% have a 5-year diabetes risk of 25-50% and 20-fold higher relative risk compared to A1C 5.0% 2.

Critical for cardiovascular risk: Prediabetes is associated with increased cardiovascular disease risk and mortality, with excess absolute risk of 7.36 per 10,000 person-years for mortality and 8.75 per 10,000 person-years for cardiovascular disease 6. Once prediabetes is identified, assess and treat other cardiovascular risk factors 7, 2.

Pediatric Considerations

In children and adolescents, consider testing after puberty onset or age 10 years (whichever is earlier) if they have overweight (≥85th percentile) or obesity (≥95th percentile) plus ≥1 risk factor 5, 1:

• Maternal diabetes/gestational diabetes during gestation
• Family history of type 2 diabetes in first- or second-degree relative
• High-risk race/ethnicity
• Signs of insulin resistance (acanthosis nigricans, hypertension, dyslipidemia, PCOS)