- 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
HgbA1c
(%) | MBG
(mg/dL) | Average plasma glucose
(mg/dL) |
|---|
| 4 | 61 | 65 |
| 5 | 92 | 100 |
| 6 | 124 | 135 |
| 7 | 156 | 170 |
| 8 | 188 | 205 |
| 9 | 219 | 240 |
| 10 | 251 | 275 |
| 11 | 283 | 310 |
| 12 | 314 | 345 |
- 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.
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
- Insulin antibodies
- Ketones
- Microalbumin
- Triglycerides
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
| Conv. Units
(%) | SI Units
(Fraction) |
|---|
| Normal (not diabetic) | <5 | <0.05 |
| Diabetics (Goal) | <7 | <0.07 |
| Diabetics (Poor control) | >7 | >0.07 |
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
Conditions associated with decreased HgbA1C include:
- Hemolytic anemia
- Chronic blood loss
- Pregnancy
- Acute caloric restriction
- Artifactual decrease
- Drugs
- Acarbose
- Carbamate
- Deferoxamine
- Diltiazem
- Enalapril
- Galactose
- Glipizide
- Glyburide
- Insulin
- Lisinopril
- Metformin
- Nisoldipine
- Pravastatin
- Ramipril
- Terazosin
- Verapamil