Yes, an A1c of 5.9% meets the diagnostic criteria for prediabetes.
According to the most recent 2025 American Diabetes Association guidelines, prediabetes is defined as an A1c between 5.7-6.4% (39-47 mmol/mol), and your patient's A1c of 5.9% falls squarely within this range 1.
Diagnostic Criteria
The 2025 ADA Standards of Care clearly establish three ways to diagnose prediabetes 1:
- Fasting plasma glucose: 100-125 mg/dL
- 2-hour oral glucose tolerance test: 140-199 mg/dL
- A1c: 5.7-6.4%
Your patient meets the A1c criterion definitively.
Risk Stratification Within Prediabetes
While she has prediabetes, it's important to recognize that her A1c of 5.9% places her in the "lower" prediabetes range (5.7-6.0%) rather than "higher" prediabetes (6.1-6.4%), which carries different risk profiles 2:
- 10-year diabetes risk: Patients with A1c 5.7-6.0% have approximately 4-fold increased risk of developing diabetes compared to normal A1c
- 10-year ASCVD risk: Modestly elevated (HR 1.08-1.18) compared to normal A1c
- Those with A1c 6.1-6.4% face dramatically higher risks (14-15 fold for diabetes, HR 1.25-1.27 for ASCVD)
Clinical Implications and Management Priority
The diagnosis of prediabetes should trigger annual A1c monitoring 1. The 2025 guidelines explicitly state that people with prediabetes (A1c ≥5.7%) should be tested yearly.
Key Management Considerations:
Assess abdominal obesity status immediately. Research demonstrates that waist circumference significantly modifies diabetes risk even in lower-range prediabetes 2. Women with A1c 5.7-6.0% and increased waist circumference show meaningfully elevated progression to diabetes, making weight management a critical intervention target.
Prioritize lifestyle modification as first-line therapy, focusing on:
- Weight reduction if overweight/obese
- Physical activity
- Dietary modification
Screen for additional cardiovascular risk factors including hypertension, dyslipidemia, and family history, as prediabetes confers increased ASCVD risk independent of glucose levels 2.
Important Caveats
The A1c criterion identifies different patients than glucose-based testing. Studies show only 55% concordance between A1c and glucose criteria for prediabetes 3. Patients diagnosed by A1c alone tend to be older, more likely female, and have different metabolic profiles than those identified by fasting glucose. This doesn't invalidate the diagnosis—it simply means A1c captures a distinct at-risk population.
Consider confirmatory testing with fasting glucose or OGTT if clinical suspicion differs from A1c result, particularly in populations where A1c may be less reliable (hemoglobinopathies, anemia, recent blood loss). However, the positive predictive value of A1c 5.7-6.4% for true dysglycemia is only 39% when confirmed by OGTT 4, so some patients may have normal glucose tolerance despite elevated A1c.
Ensure adequate carbohydrate intake (at least 150 g/day for 3 days) preceded the A1c test if you plan confirmatory glucose testing 1.