Synonym

• HgbA1C
• A1C
• Glycosylated hemoglobin
• Glycohemoglobin
• Glycated hemoglobin

Tubes

• Lavender top tube preferred; green top acceptable
• 5 mL of venous blood

Additional information

• Blood sample can be drawn at any time
• Store in refrigerator until sent to the laboratory

Info

• HgbA1C measures the concentration of glycosylated hemoglobin in the blood
• HgbA1C is the standard test for monitoring long term glycemic control for patients with either type 1 or type 2 diabetes mellitus
• The value of HgbA1C reflects the average blood sugar level for the prior 2-3 months
• Approximately 8% of hemoglobin A is made up of minor components that are chemically slightly different. They include: hemoglobin A1c, A1b, A1a1, and A1a2.
• Glycosylated hemoglobin is the hemoglobin (Hgb) in the RBC that has become spontaneously bound to glucose, through a nonenzymatic process, during its 120-day circulating life span.

Detailed information on this test

• HgbA1C values are not subject to the fluctuations seen with daily blood glucose monitoring, but instead reflect average levels for the prior 2-3 months
• HgbA1C is formed at a rate proportional to the average glucose concentration and the mean blood glucose (MBG) concentration can be estimated from the HgbA1C using this equation:

MBG (mg/dL) = 33.3 × [HgbA1c (%)] – 86

• The Rohlfing formula using Mean Plasma Glucose (MPG) and conventional units is: MPG (mg/dL) = [HgbA1C (%) × 35.6]-77.3
• Various methods are used to measure HgbA1c such as
• Affinity chromatography
• Cation exchange chromatography
• HgbA1c electrophoresis
• HPLC
• Immunoassay technique
• Hemoglobins F, S and C of various hemoglobinopathies do not interfere with the measurement of glycohemoglobin by affinity chromatography, but may interfere in the electrophoretic techniques.
• Conditions where the number of beta-chains iseither abnormal or reduced will lead to false low results by immunoassay technique.

Clinical

The clinical utility of the HbA1c test includes:

• In newly diagnosed diabetics, this test reflects how poorly controlled their blood glucose has been in the preceding 2-3 months
• In established diabetics, to monitor average glycemic control for the preceding 2-3 months
• To evaluate therapeutic efficacy of diabetic treatment modalities, usually every 3 months

Treatment and Testing Guidelines

• The American Diabetes Association (ADA) recommends the following use of the HgbA1C test:
• Testing 4 times a year, if a person has type 1, or type 2 diabetes and uses insulin
• Testing 2 times a year, if a person has type 2 diabetes and does not use insulin
• Reevaluation of treatment in people with values consistently >8%
• The goal of diabetic therapy is to maintain HgbA1C levels at <7%
• The Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS) studies showed that lower the HgbA1C value, the greater the chances to slow or prevent the development of serious eye, kidney and nerve disease

Additional information

• Not of much value in well controlled diabetics
• Lower in men with diabetes than in women with diabetes
• Increases with age
• Interfering factors:
• Shortened RBC Lifespan
• Hemolytic States
• Renal Disease
• Elevated HbF and H (false positive values)
• Elevated Hb S, C, E, D, G, and Lepore (false decreased values)
• Thalassemia & sickle cell anemia (false decreased values)
• Alcoholism
• Cirrhosis of Liver
• Related laboratory tests include:
• Cholesterol (total and HDL)
• C-peptide
• Fructosamine
• Glucose
• Glucose tolerance testing
• Insulin
• Ketones
• Microalbumin

Nl Result

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

High Result

Conditions associated with elevated HgbA1C include:

• Newly diagnosed diabetes
• Poorly controlled or uncontrolled diabetes
• Iron-deficiency anemia
• Splenectomy
• Uremia / renal failure
• Alcohol toxicity
• Lead toxicity
• Opiate addiction
• Hypertriglyceridemia
• Stress
• Artifactual increase
• Elevated HbF
• Thalassemia
• Sickle Cell Disease
• Hemoglobinopathies
• Hb Raleigh
• Acetylation
• Carbamylation
• Drugs
• Aspirin
• Atenolol
• Beta-blockers
• Gemfibrozil
• Glimepiride
• Hydrochlorothiazide
• Indapamide
• Insulin
• Lovastatin
• Morphine
• Niacin
• Nicardipine
• Nicotinic acid
• Propranolol
• Salicylates
• Sulfonylureas

Low Result

Conditions associated with decreased HgbA1C include:

• Hemolytic anemia
• Chronic blood loss
• Pregnancy
• Acute caloric restriction
• Artifactual decrease
• HbS (Sickle Cell)
• HbC
• Drugs
• Acarbose
• Carbamate
• Deferoxamine
• Diltiazem
• Enalapril
• Galactose
• Glipizide
• Glyburide
• Insulin
• Lisinopril
• Metformin
• Nisoldipine
• Pravastatin
• Ramipril
• Terazosin
• Verapamil

References

• Hussein OA et al. LDL oxidation is associated with increased blood hemoglobin A1c levels in diabetic patients. Clin Chim Acta. 2006 Oct 26; [Epub ahead of print]
• Josephsen G et al. Poor glycemic control in diabetic patients seeking care in the ED. Am J Emerg Med. 2006 Oct;24(6):721-4.
• Laboratory Corporation of America. Hemoglobin (Hgb) A1c. [Homepage on the internet]© 2003. Last updated on October 18, 2006. Last accessed on November 2, 2006. Available at URL: http://www.labcorp.com/datasets/labcorp/html/chapter/mono/pr012800.htm
• LabTestsOnline®. A1c. [Homepage on the Internet]© 2001-2006. Last reviewed on August 29, 2005. Last accessed on November 2, 2006. Available at URL: http://www.labtestsonline.org/understanding/analytes/a1c/sample.html
• Nakagami T et al. Is the measurement of glycated hemoglobin A1c alone an efficient screening test for undiagnosed diabetes? Japan National Diabetes Survey. Diabetes Res Clin Pract. 2006 Oct 16; [Epub ahead of print].
• O'Sullivan CJ et al. Haemoglobin A1c (HbA1C) in non-diabetic and diabetic vascular patients. Is HbA1C an independent risk factor and predictor of adverse outcome? Eur J Vasc Endovasc Surg. 2006 Aug;32(2):188-97. Epub 2006 Mar 31.
• Reynolds TM et al. The number of unexpected HbA variants may be a greater problem in routine practice than is generally realized. Diabet Med. 2004 Sep;21(9):1041-4.
• Rohlfing CL, et al. Defining the relationship between plasma glucose and HbA(1c): analysis of glucose profiles and HbA(1c) in the Diabetes Control and Complications Trial. Diabetes Care. Feb 2002;25(2):275-8.
• Sakaguchi A et al. Novel fluorescent sensing system for alpha-fructosyl amino acids based on engineered fructosyl amino acid binding protein. Biosens Bioelctron. 2006 Sep 30; [Epub ahead of print].
• Sargrad KR et al. Effect of high protein vs high carbohydrate intake on insulin sensitivity, body weight, hemoglobin A1c, and blood pressure in patients with type 2 diabetes mellitus. J Am Diet Assoc. 2005 Apr; 105(4):573-80.
• Sicard DA et al. Comparison of point-of-care HbA1c test versus standardized laboratory testing. Ann Pharmacother. 2005 Jun; 39(6):1024-8. Epub 2005 Apr 19.
• Stene LC et al. Normal but increasing hemoglobin A1c levels predict progression from islet autoimmunity to overt type 1 diabetes: Diabetes Autoimmunity Study in the Young (DAISY). Pediatr Diabetes. 2006 Oct;7(5):247-53.
• UTMB Laboratory Survival Guide®. HEMOGLOBIN A1c QUANTITATION. [Homepage on the Internet]© 2006. Last reviewed on February 1,2006. Last accessed on November 21, 2006. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/hem/hemoglobin_a1c_quantitation.htm