Blood A1c, also called hemoglobin A1c, is a test recommended by the American Diabetes Association for diabetes screening and routine monitoring. A1c is a form of hemoglobin -- a protein in red blood cells -- that has combined with a molecule of the sugar glucose. As a marker for how much glucose has been present in the blood over time, elevated A1c values are most commonly seen in people with diabetes. However, in certain medical situations, A1c may be elevated in someone who does not have diabetes.
Blood Glucose History
A1c forms naturally when glucose is present in the blood. The percentage of A1c increases in proportion to the average blood glucose level over the previous months before the sample was taken. An international expert committee published evidence in July 2009 in "Diabetes Care" that A1c may be used to reliably diagnose diabetes. According to guidelines from the American Diabetes Association, an A1c of 6.5 percent or higher suggests you may have diabetes.
An A1c value represents the percent of the total hemoglobin in the A1c form. Both an increase of A1c hemoglobin -- due to the presence of high blood sugar -- or a decrease in total hemoglobin can make the A1c percentage higher. Certain types of anemia associated with low total hemoglobin production can elevate the proportion of hemoglobin present in the A1c form. People with anemia due to lack of iron, folate or vitamin B12 may have an elevated A1c without having diabetes. Anemia caused by certain types of untreated kidney disease may also cause an elevated A1c in the absence of diabetes.
People with genetic conditions that affect the composition of their hemoglobin proteins may have high A1c values without diabetes. Examples of genetic conditions that may cause a falsely elevated A1c value include sickle cell trait and S-beta-thalassemia. However, several genetic blood disorders that cause premature red blood cell breakdown commonly cause low A1c values.
Certain medications may cause high blood sugar values in people who do not have diabetes. If taken for a prolonged period, these drugs may lead to an elevated A1c in the absence of underlying diabetes. Examples include corticosteroids, such as prednisone, and the antiseizure medication phenytoin (Dilantin). Some antiviral medications used to treat human immunodeficiency virus can also elevate blood sugar, including fosamprenavir (Lexiva) and saquinavir (Invirase). Drugs used after organ transplantation may suppress hemoglobin production and cause an increase in A1c without diabetes.
Different laboratory methods are used to measure A1c and calculate the A1c value. Some test methods give a higher A1c value than others. Certain chemicals in the blood formed naturally or from the use of medicines may also interfere with the test. Discuss factors that may influence A1c with your doctor.
- Diabetes Care: International Expert Committee Report on the Role of the A1C Assay in the Diagnosis of Diabetes
- International Journal of Diabetes in Developing Countries: Hemoglobin Variants Detected by Hemoglobin A1c (HbA1c) Analysis and the Effects on HbA1c Measurements
- Diabetes: Hemoglobin A1c in Diabetes -- Panacea or Pointless?
- National Diabetes Information: Causes of Diabetes
- Diabetes Care: Standards of Medical Care in Diabetes -- 2013
- National Glycohemoglobin Standardization Program: Factors That Interfere With HbA1c Test Results
- Journal of the American Society of Nephrology: Diagnostic Application of the A1c Assay in Renal Disease
- World Journal of Diabetes: Hemoglobin A1c in Early Postpartum Screening of Women with Gestational Diabetes
- Clinica Chimica Acta: Falsely Elevated Hemoglobin A1c Due to S-Beta+-Thalassemia Interference in Bio-Rad Variant II Turbo HbA1c Assay
- GlobalRPH: Hyperglycemia -- Drug Induced