When diagnosing diabetes, an elevated level should be confirmed with repeat testing, except in symptomatic patients and who have plasma glucose >200 mg/dl. 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.
HPLC HbA1c method does not shows any interference for hemoglobin variants, heterozygous HbS, HbC and HbD and HbF <=25%( Elevated HbF can be identified in HPLC methods but not in immunoassays). HbE shows interference with HPLC method and falsely lowers the HbA1c. Other variants may also show interference. In patients with homozygous forms of variant Hb (e.g. SS, CC, EE) SC), there is no HbA thus no HbA1c values cannot be quantitated using this method. In such situations fructosamine should be used as an alternate method for monitoring glycemic control.