What is the appropriate next step for an adult without a known diabetes diagnosis who has a hemoglobin A1c of 6.3%?

Diagnosis of Prediabetes and Next Steps

An HbA1c of 6.3% establishes the diagnosis of prediabetes, and you should immediately initiate intensive lifestyle intervention targeting 5–10% weight loss, confirm the diagnosis with a repeat HbA1c or fasting glucose within 3 months, and consider metformin if the patient has additional risk factors such as BMI ≥35 kg/m², age <60 years, or prior gestational diabetes. 1

Diagnostic Classification

• HbA1c 6.3% falls within the prediabetes range (5.7–6.4%), which identifies individuals at increased risk for developing type 2 diabetes and microvascular complications 1, 2
• This level does not meet the diagnostic threshold for diabetes (HbA1c ≥6.5%) 1, 2
• The patient has approximately a 3-fold increased risk of developing diabetes within 6 years compared to individuals with HbA1c <5.6% 3

Confirmation Testing

• Repeat HbA1c testing within 3 months to confirm the diagnosis, as a single elevated value may reflect laboratory variation or transient hyperglycemia 1
• Alternatively, confirm with fasting plasma glucose (FPG) if HbA1c testing has limitations in this patient (e.g., hemoglobinopathy, recent blood transfusion, severe anemia) 4
• If FPG is <100 mg/dL but HbA1c remains 6.0–6.4%, the patient still has prediabetes and warrants intervention 1

Immediate Lifestyle Intervention (First-Line Therapy)

• Prescribe a structured lifestyle program targeting 7% body weight reduction through caloric restriction (500–750 kcal/day deficit) and ≥150 minutes/week of moderate-intensity physical activity 1
• Achieving 5–10% weight loss lowers HbA1c by 0.6–1.0% and reduces progression to diabetes by 58% 1
• Refer to a Diabetes Prevention Program (DPP) or similar evidence-based behavioral intervention if available 1

Pharmacologic Therapy Consideration

• Metformin 850 mg twice daily should be considered for prediabetes if the patient meets any of the following high-risk criteria: 1
  • BMI ≥35 kg/m²
  • Age <60 years (younger individuals have longer duration of prediabetes exposure)
  • Prior gestational diabetes
  • Rising HbA1c despite lifestyle intervention (e.g., HbA1c increases from 6.0% to 6.3% over 1 year)
• Metformin reduces diabetes incidence by 31% in high-risk prediabetes populations 1
• Do not initiate other glucose-lowering agents (sulfonylureas, DPP-4 inhibitors, SGLT2 inhibitors, GLP-1 agonists, or insulin) at this HbA1c level, as they are not indicated for prediabetes 1

Monitoring Schedule

• Recheck HbA1c every 6–12 months to assess progression and response to lifestyle intervention 1, 2
• If HbA1c rises to ≥6.5% on repeat testing, the patient meets criteria for type 2 diabetes and requires initiation of metformin plus intensified lifestyle therapy 1
• If HbA1c remains 6.0–6.4% after 3–6 months of lifestyle intervention, add metformin if not already started 1

Cardiovascular Risk Factor Management

• Screen for and aggressively treat hypertension (target <130/80 mmHg), dyslipidemia (consider statin if 10-year ASCVD risk ≥7.5%), and smoking 1
• These interventions provide greater mortality benefit than glucose lowering alone in the prediabetes range 1

Common Pitfalls to Avoid

• Do not dismiss HbA1c 6.3% as "borderline" or "not quite diabetes"—this level confers significant future diabetes risk and warrants immediate action 3
• Do not delay lifestyle intervention while waiting for confirmatory testing; begin counseling at the first visit 1
• Do not target HbA1c <5.7% with pharmacotherapy, as there is no evidence that lowering HbA1c below the prediabetes threshold in non-diabetic individuals improves outcomes 1
• Do not use HbA1c as the sole screening test in populations where it performs poorly (e.g., certain ethnicities, hemoglobinopathies)—combine with fasting glucose if clinical suspicion for diabetes is high despite HbA1c 6.0–6.4% 4, 5

Special Considerations

• If the patient is obese (BMI ≥30 kg/m²), an HbA1c of 6.3% may underestimate glucose intolerance; consider a 75-g oral glucose tolerance test (OGTT) to detect isolated postprandial hyperglycemia, as up to 53% of individuals with HbA1c 6.0–6.4% may have diabetes by OGTT criteria 5, 6
• In children and adolescents, HbA1c has poor sensitivity (68%) and specificity (78%) for prediabetes; OGTT is preferred in this population 7