Diabetes affects approximately 25 million people in the United States. This disorder causes blood sugar (glucose) levels to rise and it can have serious long-term effects such as damage to nerves, kidneys, and retinas. Oral medications and insulin are used to control blood sugar levels, which patients should measure several times each day. One of the best ways to monitor the overall control of diabetes is to test patients' levels of hemoglobin A1c, also known as glycated hemoglobin. This is a stable modified form of hemoglobin that is created by the interaction between hemoglobin and glucose in blood where hemoglobin carries oxygen. Since the lifespan of a red cell in the blood is about 120 days, the A1c level is a good indicator of the average level of glucose in the blood over the past 2 to 3 months; if the levels are too high then extra medication can be given to improve diabetes control. A1c levels are usually measured 2 to 4 times per year during a visit to the physician office, clinic, or hospital where blood is drawn and sent to a central laboratory for analysis. However, the results of this testing are often not available for several days and planning of medication changes may be improved by more rapid availability of test results. A number of A1c test systems called point-of-care devices are available for measuring A1c in a convenient clinical setting, or by patients at home.