News Release

Wednesday, November 28, 2007

People with Diabetes and Sickle Cell Trait Should Have Reliable A1C Test

Campaign Informs Physicians and Patients.

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:

  • an A1C result does not correlate with results of self blood glucose monitoring
  • an A1C result is different than expected or radically differs from a previous test result after a change in lab A1C methods
  • an A1C result is more than 15 percent.

"If you see a significant discrepancy between a patient’s A1C reading and the results of routine blood glucose monitoring, consider the possibility that your patient may have a hemoglobin variant and find out if your lab is using an accurate method to measure A1C," advises NIDDK Director Griffin P. Rodgers, M.D.

Hemoglobin is the oxygen-transporting protein in red blood cells. Mutations in the genes that code for the protein, which occur more frequently in people of African, Mediterranean, and southeast Asian descent, cause variations in the structure or amount of hemoglobin. Researchers have identified hundreds of hemoglobin variants in the human population, affecting millions of people worldwide.

The most common variant is sickle cell trait in which a person inherits a gene for hemoglobin S and a gene for hemoglobin A, the usual form of hemoglobin. Sickle cell trait affects about 8 percent of African Americans. Having sickle cell trait or another hemoglobin variant does not increase a person’s risk for developing diabetes.

In sickle cell disease, a person inherits two genes for hemoglobin S, which causes the malformation, or sickling, of red blood cells, leading to anemia, repeated infections, and periodic episodes of pain. The A1C test is not used in diabetes patients with sickle cell anemia due to the shortened life span of red blood cells.

Diabetes afflicts nearly 21 million people in the United States, but its burden is disproportionately felt by minorities, including African Americans, Hispanic/Latino Americans, American Indians and Alaska Natives, Asian Americans, and Pacific Islanders. About 13 percent of African Americans age 20 and older suffer from diabetes, a rate that is nearly twice that of non-Hispanic whites.

The NIDDK conducts and supports research on diabetes; endocrine and metabolic diseases; digestive diseases, nutrition, and obesity; and kidney, urologic and hematologic diseases. Spanning the full spectrum of medicine and afflicting people of all ages and ethnic groups, these diseases encompass some of the most common, severe, and disabling conditions affecting Americans.

For information about the CDC, an agency of the U.S. Department of Health and Human Services, see

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit

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