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Routine blood sugar measurement is necessary for patients with diabetes because it helps in planning diet, exercise, and monitoring the effects of diabetes medications. Testing also allows patients to respond quickly to high or low blood glucose levels (hyper- or hypoglycemia) by managing diet, exercise, stress, or therapy (ie. medications, mindfulness, etc). If you know what is happening with your blood sugar you are more likely to take action.
Diabetes patients should monitor blood glucose levels 1 to 2 times per day (Type 2 Diabetes), and for those who use insulin (Type 1 or Type 2) require more frequent testing, up to 6-10 times daily.
These requirements tend to put a significant burden on the patient. First, with standard glucose monitoring technology, each observation requires the patient to acquire blood, typically by finger stick. The pain and inconvenience of this process over time can reduce patient compliance with testing plans. Even with regular monitoring there is no provision for observing short, transitory changes in glucose levels. Each glucose test reported is a record of the level made at the time of measurement. Frequent testing is required to detect significant fluctuation of blood sugars that could have occurred during the course of a day. Hypoglycemic events or a sudden rise in blood sugar is likely to go undetected, and could lead to complications.
Many of the limitations of regular glucose monitoring are alleviated by the use of Continuous Glucose Monitors (CGMs) The most popular of these systems employ a small disposable probe that is placed just beneath the skin, where it is in contact with the interstitial fluid. Glucose levels in the interstitial space correlate with blood sugar, but require calibration in the form of a finger stick to ensure the interstitial sugar is similar to the blood glucose levels.
The CGM’s transdermal sensor communicates with an external transmitter that transfers readings to either a purpose-built receiver, or a smartphone application, at pre-set intervals (typically every few minutes). This produces a continuous record of blood glucose levels that can help direct decisions regarding diet, exercise, medications, etc., and can also provide a more complete picture of how blood sugar fluctuates over time.
A major advantage of using CGM is that it produces a virtually continuous record of blood glucose levels without the need to collect blood at each measurement. This can be especially useful in treatment of patients for whom very frequent testing is needed, or for whom achieving stable blood sugar levels has proven elusive. It also allows frequent measurements while minimizing the pain and potential for infection associated with finger sticks.
CGM facilitates rapid response to rising or falling blood glucose levels. In a typical system (e.g., DEXCOM G5, shown below) minimum and maximum allowable levels can be pre-set by the patient. If glucose levels fall below the lower limit or exceed the higher, an alarm sounds, warning the patient quickly so she/he can respond appropriately. The CGM also maintains a real time record of readings for a period of time, greatly facilitating adjustment of insulin or other medications to achieve stable blood glucose levels.
CGM devices are improving steadily, and represent a major advance in development of technology to monitor and control blood glucose levels. CGM is not without limitations. The cost of buying and using a CGM is high, and may limit adoption of these systems. This cost may decline over time as more manufacturers enter the market with newer CGM systems. Additionally, replacement transdermal probes are expensive, and must be changed regularly (e.g., weekly), and this contributes significantly to the cost of purchasing and using this instrumentation.
The instrumentation also requires calibration, up to twice each day. This calibration compares CGM readings with a control reading from a standard glucometer using freshly-drawn blood. Patients must therefore have access to both standard and CGM devices, increasing somewhat the complexity and cost of their treatment.
Although state-of-the-art CGM systems are not without limitations, they are being accepted widely, especially by patients who are on insulin and therefore require more frequent blood glucose monitoring. It is likely that with improvements over time, and with associated reduction in costs, CGM may become more common. It is also likely that newer technologies will reduce the cost, as well as the physical and psychological barriers to regular blood sugar measurement.