Why Is Hemoglobin A1c (HbA1c) Measured?

Last Editorial Review: 9/21/2017

Ask the experts

Why does my doctor want me to get a hemoglobin A1c (HbA1c) test?

Doctor's response

HbA1c levels depend on the blood glucose concentration. That is, the higher the glucose concentration in blood, the higher the level of HbA1c. Levels of HbA1c are not influenced by daily fluctuations in the blood glucose concentration but reflect the average glucose levels over the prior six to eight weeks. Therefore, HbA1c is a useful indicator of how well the blood glucose level has been controlled in the recent past and may be used to monitor the effects of diet, exercise, and drug therapy on blood glucose in diabetic patients.

In healthy, non-diabetic patients the HbA1c level is less than 7% of total hemoglobin. It has been demonstrated that the complications of diabetes can be delayed or prevented if the HbA1c level can be kept close to 7%. In general, values should be kept below 8%.

What are the limitations to measuring HbA1c?

Since HbA1c is not influenced by daily fluctuations in blood glucose concentration, it cannot be used to monitor day-to-day blood glucose concentrations and to adjust insulin doses nor can it detect the day-to-day presence or absence of hyperglycemia or hypoglycemia.

HbA1c may be increased falsely in certain medical conditions. These conditions include uremia (kidney failure), chronic excessive alcohol intake, and hypertriglyceridemia. Medical conditions that may falsely decrease HbA1c include acute or chronic blood loss, sickle cell disease or thalassemia. Diabetes during pregnancy, commonly referred to as gestational diabetes, may falsely increase or decrease HbA1c.

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