How often you test is determined by the kind of diabetes you have, the kind of treatment you're using, and the level of stability of your blood glucose.
If you have type 1 or type 2 diabetes and you're taking before-meal insulin, you need to test before each meal and at bedtime. The reason for this frequent testing is that you're constantly using this information to make adjustments in your insulin dose. No matter how good you think your control is, you cannot feel the level of the blood glucose without testing unless you're hypoglycemic.
People with type 1 diabetes should occasionally test one or two hours after a meal and in the middle of the night to see just how high their glucose goes after eating and whether it drops too low in the middle of the night. These results guide you and your physician to make the changes you need.
Numerous studies have shown that increased daily frequency of blood glucose testing is significantly associated with lower levels of hemoglobin A1c and fewer complications of diabetes in patients who take insulin. There is a 0.2 percent lowering of A1c for each extra test up to a maximum of five tests.
If you have type 2 diabetes and you're on pills or just diet and exercise, testing doesn't seem to make a major difference in your glucose control. In a large study, regular testing resulted in just a .25 percent reduction in hemoglobin A1c and even this improvement was gone by 12 months. The main reason is that patients don't use the test results to make changes in treatment.
The blood glucose test can be useful many other times of day in the patient on insulin:
If you eat something off your diet and want to test its effect on your glucose, do a test.
If you're about to exercise, a blood glucose test can tell you if you need to eat before starting the exercise or if you can use the exercise to bring your glucose down.
If your diabetes is temporarily unstable and you're about to drive, you may want to test before getting into the car to make sure that you're not on the verge of hypoglycemia. Even if your diabetes is stable, testing at the beginning and after every couple of hours of a long drive can prevent serious hypoglycemia.
You're not being graded on your glucose test results. The human body has too much variation in it to expect that each time you take the same medication, do the same exercise, eat the same way, and feel the same emotionally, you will get the same test result. If the person who reviews your results with you sees your abnormal results as bad, he or she does not understand this point. You may want to consider finding someone who does.
Keep in mind that the occasional blood glucose test done in your doctor's office is of little or no value in understanding the big picture of your glucose control. It is like trying to visualize an entire painting by Seurat (who painted using dots of color) by looking at one dot on the canvas.