Red blood cells carry oxygen (O2) to the tissues through the blood flow of the circulatory system (Figure 1).
When the hemoglobin binds to oxygen, the cells appear red (that is why they are called red blood cells. Red blood cells contain hemoglobin, which normally carries oxygen to the tissue, and when the hemoglobin binds with glucose in the blood, it becomes “glycated.” The term HbA1c refers to glycated hemoglobin (Figure 2). The more glycated hemoglobin that is made, the higher the percentage of HbA1c.
A hemoglobin A1c (HbA1c) test is good for monitoring long-term glucose (sugar) control in people with diabetes. HbA1c is a percentage of the glycated hemoglobin relative to the total hemoglobin in the blood (Figure 3). The normal range of HbA1c is 4-6%. More than 7% is high. With more glucose present in the blood, the more likely that the glucose will interact with the hemoglobin and make more glycated hemoglobin. HA1c is a better measurement used to track the progress of diabetes than a blood sugar test. The blood sugar test does not give the big picture.
Blood sugar in the body changes during the day depending on diet and level of activity, so the blood sugar test is not very accurate. The A1c test is used to measure how much sugar a person has in their blood over a longer period of time, which is usually 3 months. The lifespan of red blood cells is about 120 days, while the life span of hemoglobin is on average only two months (Figure 4).
The A1c test is usually done 2-4 times a year. The higher the A1c, the higher the risk of diabetic complications. A decrease of 1% in A1c decreases the risk of microvascular complication by 37%.
Diabetes is a serious disease that affects the eyes, kidneys, heart and feet (Figure 5).
How does hemoglobin work?
The red blood cells contain large quantities of proteins called hemoglobin which bind to oxygen loosely and reversibly. The hemoglobin molecules are composed of four subunits α1, α2, β1, and β2. Each hemoglobin contains four heme molecules, one attached to each subunit, and iron containing pigment that binds to oxygen (Figure 6). Oxygen molecules bind at the center of each heme molecule. Heme makes it possible for the red blood cells to pick up oxygen for delivery to the cells of the body.
Hemoglobin that is saturated with oxygen is called oxyhemoglobin and is bright red in color. Glycated hemoglobin decreases the oxygen carrying capacity and limits the tissue oxygen delivery (Figure 7).
Hemoglobin releases its oxygen when the red blood cells pass through capillaries where the oxygen then moves out of the capillaries and on to the cells where it is needed. In diabetics, glycated hemoglobin limits delivery of oxygen to the tissue (Figure 8). The tissue is not healthy and may cause a microvascular complication.
Lowering A1c levels reduces the risk of diabetic complications in patients with type 2 diabetes. A high preoperative hemoglobin A1c is a risk factor for surgical site infection after lumbar spinal instrumentation surgery and total joint replacement. In general, a surgeon will delay a joint replacement surgery until the patient’s hemoglobin is under 7%. The physician should be alert of surgical wound complications in patients with a high hemoglobin A1c test and this test should be obtained in diabetic patient before an elective surgery.
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