When diagnosing diabetes, an elevated level should be confirmed with repeat testing. American Diabetes Association (ADA) recommends HbA1c should be measured 3-4 times per year for type 1 and poorly controlled type 2 diabetes and 2 times per year for well-controlled type 2 diabetic patients.
HbA1c assay reflects long term fluctuations in blood glucose concentration, a diabetic patient who may have come in recent weeks under good control may still have a high concentration of HbA1c and conversely a diabetic patient previously under good control now poorly controlled may still have low concentrations of HbA1c.
In conditions with shortened erythrocyte lifespan (hemolytic anemia), HbA1c results will be decreased and affect will be dependent on the severity of anemia. Patients with polycythemia or post-splenectomy may exhibit increased HbA1c levels due to longer erythrocyte lifespan. HbA1c values in recently transfused patients may be falsely elevated.
Individuals with recent significant blood loss exhibit falsely low HbA1c values due to a higher fraction of young erythrocytes.
Abnormal life span of red blood cells as found in hemolytic anemia, polycythemia or post splenectomy may affect the levels of HbA1c.