When should you get a Hemoglobin A1c (HbA1c) test?

When to Get an A1C Test

A1C testing should be performed at least twice yearly in patients with stable glycemic control who are meeting treatment goals, and quarterly in patients whose therapy has changed or who are not meeting glycemic goals. 1, 2

Diagnostic Testing for Diabetes

Initial Screening

• For asymptomatic adults:
  • Test if overweight/obese (BMI ≥25 kg/m²) with one or more additional risk factors 1
  • Begin testing at age 45 for those without risk factors 1
  • If tests are normal, repeat at least every 3 years 1

High-Risk Populations Requiring Screening

• Age ≥40 years
• History of prediabetes (IGT and/or IFG)
• Overweight (BMI ≥24 kg/m²) or obesity (BMI ≥28 kg/m²)
• First-degree relatives with type 2 diabetes
• History of gestational diabetes (women)
• Hypertension or on antihypertensive therapy
• Dyslipidemia or on lipid-lowering therapy
• Atherosclerotic cardiovascular disease
• Polycystic ovary syndrome 1

Monitoring Frequency Guidelines

For Patients with Diabetes

1. Stable glycemic control meeting targets:

   • A1C testing every 6 months 1, 2

2. Unstable control or recent therapy changes:

   • A1C testing every 3 months 1, 2

3. Point-of-care testing:

   • Provides opportunity for more timely treatment changes 1

For Patients with Prediabetes

• A1C testing every 6 months for stable prediabetes
• Every 3 months initially for those on metformin, then every 6 months once stable 2
• Annual testing for those with risk factors but normal previous results 2

Special Considerations

When A1C May Be Inaccurate

A1C may be unreliable in conditions affecting red blood cell turnover. Use glucose criteria exclusively for diagnosis in:

• Pregnancy
• Hemolytic anemia
• Iron deficiency anemia
• Hemoglobinopathies
• Recent blood transfusions
• End-stage kidney disease 1, 2

Alternative Monitoring Methods

When A1C is unreliable, consider:

• Self-monitoring of blood glucose (SMBG)
• Continuous glucose monitoring (CGM)
• Fructosamine or glycated albumin testing 2

Common Pitfalls to Avoid

1. Insufficient monitoring - Not testing frequently enough to detect changes in glycemic control
2. Not acting on results - Failing to adjust therapy when A1C is outside target range
3. Ignoring racial/ethnic differences - A1C criterion yields different diagnostic patterns across racial and ethnic groups 3
4. Patient unawareness - Many patients don't receive recommended A1C tests because they're unaware of the recommendation or their physician didn't inform them 4

Clinical Implications

The A1C test reflects average glycemia over approximately 2-3 months and has strong predictive value for diabetes complications 1. Regular monitoring is essential for tracking disease progression and evaluating treatment efficacy, allowing for timely intervention to prevent complications.

Higher HbA1c levels (>8%) are strongly associated with increased risk of microvascular and macrovascular complications, emphasizing the importance of regular monitoring and maintaining glycemic targets 2.