HbA1c Testing Does Not Require Fasting
Patients do not need to fast before an HbA1c test—the sample can be collected at any time of day regardless of when the patient last ate. 1, 2
Why Fasting Is Unnecessary
HbA1c measures average glucose levels over the preceding 2-3 months by reflecting glucose bound to hemoglobin over the 120-day lifespan of red blood cells, making it fundamentally different from point-in-time glucose measurements. 1, 2
Key Advantages Over Fasting Tests
The test result is unaffected by recent food intake, stress, acute illness, or physical activity—factors that significantly impact fasting plasma glucose (FPG) and oral glucose tolerance tests (OGTT). 1
Greater preanalytical stability and lower day-to-day variability compared to glucose measurements, which require fasting or timed samples and show high within-person variability. 1
Greater clinical convenience as the test can be drawn during any clinical encounter, including acute care settings, without concern for meal timing. 1, 2
Important Clinical Caveats
When HbA1c Results May Be Unreliable
In conditions that alter red blood cell turnover, plasma glucose criteria should be used instead of HbA1c for diagnosis: 1
Conditions that falsely elevate HbA1c (prolonged RBC lifespan): iron deficiency anemia, vitamin B12 deficiency, splenectomy 2
Conditions that falsely lower HbA1c (increased RBC turnover): pregnancy (second and third trimesters), hemodialysis, recent blood loss or transfusion, hemolysis, erythropoietin therapy, chronic liver disease, splenomegaly 1, 2
Do not use HbA1c for diagnosis in patients with hemoglobin variants (sickle cell disease, thalassemia), glucose-6-phosphate dehydrogenase deficiency, or HIV. 1, 2
Laboratory Requirements
The test must be performed using a method certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized to the Diabetes Control and Complications Trial (DCCT) reference assay. 1
Point-of-care HbA1c assays should not be used for diagnostic purposes—only laboratory-based testing in CLIA-certified facilities performing moderate complexity testing or higher is appropriate for diagnosis. 1, 2
Point-of-care assays may be used for monitoring glycemic control in established diabetes, but only if FDA-approved for that purpose and performed in appropriately certified settings. 1
Clinical Bottom Line
The non-fasting nature of HbA1c testing represents a major practical advantage over glucose-based tests, eliminating scheduling barriers and improving patient compliance while providing a more stable measure of long-term glycemic control. 1