People With Diabetes, Sickle Cell Trait Should Have Reliable A1C Test

Armen Hareyan's picture

A new information campaign of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health, highlights the importance of using accurate methods to test hemoglobin A1c in people with diabetes who have sickle cell trait or other inherited forms of variant hemoglobin. The specific needs for testing blood glucose control in these patients are explained in two booklets, "Sickle Cell Trait and Other Hemoglobinopathies and Diabetes: Important Information for Physicians" and "For People of African, Mediterranean, or Southeast Asian Heritage: Important Information about Diabetes Blood Tests" from NIDDK�s National Diabetes Information Clearinghouse at

Studies have repeatedly shown that intensive control of blood glucose, blood pressure, and cholesterol reduces heart disease and the other complications of diabetes. The hemoglobin A1c blood test (or simply the A1C test) is an essential tool in diabetes care because it shows a patient�s average level of blood glucose control in the previous 2 to 3 months. Physicians base their treatment decisions in large part on the A1C test results. Inaccurate A1C readings, whether falsely high or low, may lead to the over treatment or under treatment of diabetes.

The A1C test, though essential in diabetes management, is not recommended for diagnosing diabetes. However, if an A1C test is given to a person not known to have diabetes and the result is higher than normal, a fasting blood glucose test is needed to confirm a diabetes diagnosis.


The National Glycohemoglobin Standardization Program (NGSP) at the University of Missouri School of Medicine, supported by the NIDDK and Centers for Disease Control and Prevention (CDC), is working to improve and standardize the measurement of A1C in laboratories around the world. The NGSP website ( lists the test methods that accurately measure A1C in patients with hemoglobin variant S, also known as sickle cell trait, and variant C, another common variant in the United States.

"In the United States, more than 3,000 labs rely on 20 different methods to measure A1C in people with diabetes," says Randie Little, Ph.D., who heads the NGSP. "However, six of these methods yield unreliable results in patients with sickle cell trait. Health care professionals caring for people with diabetes should know that specific A1C tests should be used in this group of patients."

Many individuals are unaware they have a hemoglobin variant such as sickle cell trait because the condition usually causes no symptoms. In diabetes patients of African, Mediterranean, or southeast Asian descent, several situations may suggest the presence of a hemoglobin variant: