The glycosylated hemoglobin test evaluates your patient’s response to diabetes therapy. The test measures the degree to which glucose attaches to hemoglobin (a process called glycosylation). Glycosylation occurs continually during the 120-day life of a red blood cell (RBC). The higher the blood glucose level, the greater the attachment. Once glucose attaches to hemoglobin, the process is nearly irreversible, which makes the glycosylated hemoglobin test an accurate reflection of your patient’s average blood glucose level during the 4 to 8 weeks before the test.The test values are given as a percentage of the total hemoglobin within an RBC. Three he­moglobins can be measured as Ala, Alb and Alc. The hemoglobin most commonly measured is Alc because it’s normally present in the largest quantity (3% to 6% of total hemoglobin). Ala is typically 1.6%, Alb is 0.8%. The closer to normal the patient can maintain her blood glucose level over an extended period, the closer to normal her glycosylated hemoglobin will be.

Nursing considerations

If your patient uses insulin, she should have a glycosylated hemoglobin test every 3 months. For patients who don’t use insulin, the frequency of the test depends on their response to therapy, which is determined by fasting blood glucose levels.

Your patient needs no preparation before the test. If you’re collecting the specimen, perform a venipuncture and collect the blood in a 5-ml lavender-top tube. Make sure the tube fills completely. Then gently invert it several times to mix the blood and anticoagulant adequately. If hemolysis occurs, collect a new specimen.

If the glycosylated hemoglobin value is elevated but the patient reports normal blood glucose levels from her self-monitoring tests, perform a second glycosylated hemoglobin test to rule out collection or laboratory error. If the second test is consistent with the first, evaluate the patient’s self-monitoring technique and correct any errors. If the patient’s technique is correct, the problem may be that she’s reporting normal values even though her tests reveal elevated glucose levels. Try to make your patient comfortable enough to express any problems she’s encountering in trying to comply with her treatment plan, and emphasize the importance of blood glucose control in delaying the development of long-term complications.