Glycosylated hemoglobin
Alternative names:
diabetic control index; GHb; glycohemoglobin; Hb A1c; hemoglobin - glycosylated
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:
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 in individuals with diabetes mellitus.
In normal individuals a small percentage of the hemoglobin (Hb) molecules in red blood cells become glycosylated (that is, chemically linked to glucose). Glycosylated hemoglobin can be separated from normal HbA by electrophoresis (a laboratory technique) into 3 fractions called HbA1a, HbA1b, and HbA1c. Normally only HbA1c is quantitated. 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.
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