Glucose Monitoring and CGMS

A continuous glucose monitoring system takes home blood glucose monitoring to the next step. Modern continuous glucose monitoring systems consist of a small electrode inserted beneath the skin (like an insulin pump catheter), which will sense the glucose level as an electrical signal and send the information to a transmitter stuck on the skin surface. This transmitter, which can vary in size from a large coin to a small remote control key fob, will then usually transmit the information wirelessly to a recording device, which then stores the information for the next 3-5 days for later download. Certain models of CGMS can also give REAL-Time results. The machine will average out the readings every 5-10 minutes and display the number on readout.  The patient can then use this REAL-Time information to fine tune the insulin dose given, or to find out when and why he or she is getting troublesome highs and lows on the current oral medications or insulin therapy as the case may be.

CGMS systems on the market include ones by Medtronic, Abbott and Dexcom, but currently only Medtronic's system is available in Singapore.

Because blood glucose levels are always changing, a programme of carefully timed fingerstick blood glucose tests will help you and your diabetes physician adjust therapy for your maximum benefit. Popular multiple fingerstick/day protocols include the 7 - point monitoring (before and after breakfast, lunch and dinner and once more before bedtime or in the early hours of the morning) or the 5 - point monitoring (before each main meal, before bedtime and once in the early hours of the morning) or more frequently, a 3-4 times a day protocol focusing on finding out the pre-breakfast and one pre and one post meal glucose reading each day.

However, even a multiple fingerstick a day blood glucose monitoring scheme will not be practical for picking up unforeseen hypoglycemic or hyperglycemic episodes because most people will not be comfortable with doing hourly blood glucose tests for 3 days in a row. It is also not realistic, because if you are really doing hourly fingersticks for 3 days in a row, you will probably not be following your normal daily schedule, and this would limit the usefulness of such an exercise.

What about the HbA1c?

The HbA1c test is a measure of the average blood glucose reading over an approximately 3 month period prior to the test.

It can be done on a fingerprick sample of blood and is an excellent test to measure the degree of overall glucose control but it is not a perfect measure of glycemic control because you can get the same HbA1c level with the same mean blood glucose level, regardless of whether your blood glucose levels were mostly a certain level, not very high or low, and if your had the same mean blood glucose level, but blood glucose levels were fluctuating wildly with very high and very low blood glucose levels.

Although 2 people could have the same HbA1c level, the person with more fluctuations would have more complications, as has been shown in data from the landmark DCCT study.

Hence, for the person with diabetes who wishes to have the most accurate picture of his or her glycemic control, a combination of fingerstick home blood glucose monitoring, HbA1c and CGMS will give the most accurate and cost effective solution.