Measuring blood sugar with glucose sensor is used parallel with and as a replacement for traditional blood sugar testing. Glucose sensor entails measuring the glucose level of the interstitial fluid of the subcutaneous tissue over a certain period of time or on an ongoing basis (also called Continuous Glucose Monitoring or CGM). The result from glucose sensor is not entirely analogous with blood sugar testing. However, it is adequately accurate to reflect the blood sugar level when blood sugar is even, such as before eating. That is why the glucose sensor reading can also be used to estimate a mealtime insulin dose.
In addition to or instead of a single blood sugar reading, it is more useful to observe the direction and speed of the change in blood sugar as well as recurring blood sugar trends, in other words, the way blood sugar behaves repeatedly at different times of the day.
In principle, continuous glucose monitoring can be used by anyone with diabetes who is able to learn and understand the operation, use and limitations of the sensor. In practice, considering the costs, the most viable use of glucose sensor is for MDI or pump therapy.