When should A1c (glycated hemoglobin) levels be checked in patients with hyperglycemia (elevated glucose levels)?

When to Check A1c in Patients with Elevated Glucose

A1c testing should be performed routinely in all patients with elevated glucose, first to document the degree of glycemic control at initial assessment, and then quarterly for patients not meeting glycemic goals or with therapy changes, or at least twice yearly for those with stable glycemic control meeting treatment targets. 1, 2

Initial Diagnosis and Assessment

When elevated glucose is detected, A1c should be checked immediately as part of the diagnostic workup:

• Diagnostic criteria using A1c:

  • Normal: A1c < 5.7%
  • Prediabetes: A1c 5.7-6.4%
  • Diabetes: A1c ≥ 6.5% 2

• Alternative diagnostic criteria for diabetes:

  • Fasting glucose ≥126 mg/dl
  • 2-hour post-load glucose ≥200 mg/dl during OGTT
  • Random glucose ≥200 mg/dl with classic symptoms of hyperglycemia 2

Follow-up A1c Testing Schedule

The frequency of A1c testing should follow this algorithm:

1. For patients meeting treatment goals with stable glycemic control:

   • Test at least twice yearly (every 6 months) 1, 2

2. For patients NOT meeting glycemic goals or with therapy changes:

   • Test quarterly (every 3 months) 1, 2

3. For special populations requiring more intensive monitoring:

   • Pregnant women with diabetes
   • Patients with highly intensive insulin management
   • Patients with recent therapy adjustments
   • Test more frequently than every 3 months 1

Clinical Utility of A1c Testing

A1c provides valuable information that spot glucose measurements cannot:

• Reflects average glycemia over preceding 2-3 months 1, 2
• Correlates with risk of diabetes complications 1
• Helps detect departures from target glycemic range 1
• Serves as a check on accuracy of patient's self-monitoring 1

Correlation Between A1c and Average Glucose

Understanding this relationship helps interpret results:

A1c (%)	Mean Plasma Glucose (mg/dl)
6	135
7	170
8	205
9	240
10	275
11	310
12	345

1, 2

Important Considerations and Limitations

• Point-of-care A1c testing allows for timely treatment decisions but is not recommended for diagnostic purposes 2

• A1c may be unreliable in conditions affecting red blood cell turnover:

  • Hemolytic anemia
  • Blood loss
  • Recent transfusions
  • Hemoglobinopathies
  • Erythropoietin therapy 1, 2

• In these cases, alternative methods such as glycated serum protein (GSP) or fructosamine may be considered to assess glycemic control 1

• For patients with glycemic variability (especially type 1 diabetes or severe insulin deficiency), A1c should be combined with self-monitoring blood glucose results for optimal assessment 1

Treatment Targets and Adjustments

• General A1c target: <7% for most adult patients 2
• Consider treatment adjustment if A1c is between 7-8% 2
• Significantly modify regimen if A1c >8% 2
• Less stringent targets (such as <8%) may be appropriate for patients with:
  • History of severe hypoglycemia
  • Limited life expectancy
  • Advanced complications
  • Extensive comorbidities
  • Long-standing difficult-to-control diabetes 2

By following this structured approach to A1c testing in patients with elevated glucose, clinicians can optimize diagnosis, treatment decisions, and long-term monitoring to reduce morbidity and mortality associated with diabetes.