Glycosylated hemoglobin |
| Definition: |
| A blood test that measures the amount of glycosylated hemoglobin. |
| Alternative Names: |
| Hb A1c; Hemoglobin - glycosylated; GHb; Glycohemoglobin; Diabetic control index |
| How the test is performed: |
| Adult or child: Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding. Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. |
| How to prepare for the test: |
| No fasting is necessary. Infants and children: The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed: |
| This test is used to measure blood sugar control over an extended period in individuals with diabetes mellitus. In general, the higher the glycosylated hemoglobin, the higher the risk that a patients will develop complications from the diabetes (eye disease, kidney disease, nerve damage, heart disease, and stroke). On the other hand, the closer the value is to normal, the risk of these complications decreases. In normal individuals a small percentage of the hemoglobin (Hb) molecules in red blood cells become glycosylated (that is, chemically linked to glucose). The percent of glycosylation is proportional to time and to concentration of glucose. In other words, older red blood cells will have a greater percent of GHb and poorly-controlled diabetics (with periods of time where they have high concentrations of blood glucose) will have a greater percent of GHb. |
| Normal Values: |
| Glycosylated hemoglobin that is 2.2 to 4.8% of total Hb is normal, although normal ranges may vary slightly depending on the laboratory used. |
| What abnormal results mean: |
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Inadequate regulation of blood glucose levels over a period of weeks to months (poorly controlled diabetes mellitus). Higher values mean the patient is at higher risk of diabetic complications. Lower values decrease the risk. Your doctor should obtain this test every 3 to 6 months to see how well controlled your diabetes is. In general, a value less than 4.5% is ideal. A value greater than 6.1% should prompt a change in your diabetes regimen. These targets may be increased somewhat if you have frequent episodes of low blood sugars (hypoglycemia). |
| What the risks are: |
| Special considerations: |
| Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
Reviewed By: Todd T. Brown, M.D., Division of Endocrinology and Metabolism, Johns Hopkins University, Baltimore, MD. Review provided by VeriMed Healthcare Network.
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