Accuracy of Testing Sites for Diabetics

Perhaps you are one of many people suffering from sore fingertips who were delighted at the chance to use any site other than your fingertips to check your blood glucose levels. Today there are a number of meters that offer alternate-site testing. But, are the results as accurate?

The forearm is the alternative area of the body now being used most often, although the hand, upper arm, thigh, and calf can also be used. These are larger areas with fewer nerve endings. Therefore, a lancet puncture provides less discomfort than on the fingertip.

The rate of blood flow to the finger is much faster than to the arm. Therefore, when glucose levels are changing rapidly, there may be a major difference in the glucose reading between the arm and finger. Some reports have reported as much as a 100 mg/dl difference. When blood glucose is falling rapidly, the higher reading from the arm could result in a delay in treating hypoglycemia (low blood glucose).

When checking before meals, the difference is minor since glucose levels are fairly steady. Up to two hours after meals and after exercise, however, blood glucose levels are changing rapidly again. Therefore, if you choose to use an alternate site instead of the fingertips, do so only at the following times to ensure accuracy:

fasting or before a meal
two hours or more after a meal
two hours or more after exercises

At times when your blood glucose levels are changing rapidly, use your fingertips to check your blood glucose to be safe. This includes up to two hours after injecting rapid-acting insulin, up to two hours after eating a meal, and during or after exercise. It is also best to use your fingertips when monitoring before driving and during illness. If you have a history of not noticing when you are hypoglycemic (have low blood glucose), you should always use fingertip checks.

Alternate site testing offers a way to check blood glucose levels with less discomfort than the traditional method. If it helps you monitor more frequently to improve your diabetes control, it is well worth using. Remember to use alternate sites only at recommended times to ensure accuracy.

Debbie Wilburn is County Agent/Family and Consumer Science Agent with the Hall (770)535-8290 and the Forsyth (770)887-2418 County Extension Service.