Sampling blood from alternative sites may be desirable, but it may have some limitations. Blood in the fingertips show changes in glucose levels more quickly than blood in other parts of the body. This means that alternative site test results may be different from fingertip test results not because of the meter's ability to test accurately, but because the actual glucose concentration can be different. FDA believes that further research is needed to better understand these differences in test values and their possible impact on the health of people with diabetes.
Glucose concentrations change rapidly after a meal, insulin or exercise. Glucose levels at the alternative site appear to change more slowly than in the fingertips. Because of this concern, FDA has now requested that manufacturers either show their device is not affected by differences between alternative site and fingertip blood samples during times of rapidly changing glucose, or alert users about possible different values at these times.
Recommended labeling precautions include these statements:
- Alternative site results may be different than the fingertip when glucose levels are changing rapidly (e.g. after a meal, taking insulin or during or after exercise).
- Do not test at an alternative site, but use samples taken from the fingertip, if
- you think your blood sugar is low,
- you are not aware of symptoms when you become hypoglycemic, or
- the site results do not agree with the way you feel.
