Prediabetic A1C Range
An A1C level between 5.7% and 6.4% (39-47 mmol/mol) defines prediabetes according to the American Diabetes Association. 1
Complete Glycemic Criteria for Prediabetes
Prediabetes can be diagnosed using any one of three glycemic measurements 1:
- A1C: 5.7–6.4% (39–47 mmol/mol)
- Fasting Plasma Glucose (FPG): 100–125 mg/dL (5.6–6.9 mmol/L), termed impaired fasting glucose (IFG) 1
- 2-hour Plasma Glucose during 75-g OGTT: 140–199 mg/dL (7.8–11.0 mmol/L), termed impaired glucose tolerance (IGT) 1
Risk Stratification Within the Prediabetic Range
The risk of progression to diabetes is continuous throughout the prediabetic spectrum, with disproportionately greater risk at the higher end 1:
- A1C 5.5–6.0%: 5-year diabetes incidence of 9–25% 1
- A1C 6.0–6.5%: 5-year diabetes incidence of 25–50%, with a 20-fold higher relative risk compared to A1C of 5.0% 1
- A1C ≥5.7%: Associated with diabetes risk similar to high-risk participants in the Diabetes Prevention Program 1
Critical Clinical Caveats
Diagnostic Limitations of A1C for Prediabetes
While A1C is convenient and guideline-endorsed, important limitations exist:
- A1C has lower sensitivity than glucose-based testing, particularly in non-Hispanic whites, detecting only 23.6% of at-risk individuals overall (9.9% in non-Hispanic whites vs. 31.4% in African Americans) 2
- Low positive predictive value in clinical practice: Only 39.4% of patients with A1C 5.7–6.4% had confirmed prediabetes on oral glucose tolerance testing, with 48.5% having normal glucose tolerance 3
- A1C 5.7–6.4% does not reliably identify impaired insulin action or secretion, the classical pathophysiologic defects of prediabetes 4
When to Confirm with Glucose Testing
If A1C shows prediabetes (5.7–6.4%), consider confirming with fasting glucose or OGTT before initiating therapeutic interventions, particularly in 4, 3:
- Non-Hispanic white patients (lower detection rate) 2
- Patients without typical metabolic syndrome features 4
- Clinical scenarios where treatment decisions hinge on the diagnosis 3
Conditions Affecting A1C Accuracy
A1C may not accurately reflect glycemia in 5:
- Hemolytic anemia or recent blood transfusion 5
- Hemoglobin variants 5
- Racial/ethnic differences (African Americans may have higher A1C for the same mean glucose) 5
Therapeutic Implications
For patients with confirmed prediabetes, intensive lifestyle modification is first-line therapy, reducing diabetes incidence by 6.2 cases per 100 person-years over 3 years 6. Metformin is most effective for 6:
- Women with prior gestational diabetes 6
- Individuals <60 years with BMI ≥35 6
- Fasting plasma glucose ≥110 mg/dL or A1C ≥6.0% 6
Prediabetes confers increased risk not only for diabetes progression (10% annually in the US) but also for cardiovascular events and mortality 6.