So successful has this technology been that this is a difficult question to answer specifically because there are up to 20 approved glucose monitors for use at any one time, with new or updated models appearing frequently.
Also, different features are important to different individuals, depending on their needs. Probably the best way to answer this question is to discuss some of the available features.
Size is one of the first that springs to mind. Monitors have been getting ever smaller since they first appeared more than 30 years ago.
It is now possible to get a monitor that is about the same size as a standard lipstick e.g., One Touch Ultra-Mini and is yet highly functional.
Memory size is not as important as it might at first seem. A memory of about 100 readings is probably sufficient, although almost every monitor now has more.
There is limited practical usefulness of going back too far, since treatment decisions should be based on recent information, rather than distant data.
Sample size is sometimes important and most available meters now use much smaller blood samples than was previously the case.
Micro sample meters such as some Freestyle and one Touch models use samples less than 1/50th the size of an actual droplet of blood.
Many monitors will permit sampling from sites other than the fingertip, such as the forearm (most) and palm, which is useful for those with sensitive fingers or for people who are heavily involved in manual or delicate work.
The speed of obtaining the reading is now usually around 5 seconds after the blood sample is applied, although some models (such as the Prestige IQ ) can take up to 50 seconds.
This is much shorter than models in the early days, which could take from 1 to 2 minutes. Most meters can now be linked by cable, Bluetooth, or broadband to a computer and their contents are downloadable, including to the Internet.
Some meters have multistrip cassettes that dispense between 10 to 20 test strips, such as the Accuchek Compact Plus, for added convenience.
Other features include the ability to display results graphically (e.g., One Touch Ultrasmart, to function at high altitude (e.g., Advocate Duo, and to speak the results for those with limited vision (e.g., Prodigy Duo)
There are now three types of continuous glucose monitors available.
They all transmit glucose results wirelessly from a small sensor placed just beneath the skin via a transmitter whose signal is received by the monitor placed anywhere from 5 to 10 feet away.
Results are sent from every minute to every 5 minutes and the trend of the readings can be shown on graphs.
One, the Medtronic Realtime System, can transmit the results into the same unit that is used as the insulin pump.
However, even though the same unit acts as both monitor and pump, it is still necessary for the wearer to program and set the amount of insulin to be delivered.
Studies have shown that the additional information provided by the frequently delivered values and the graphed trends reduces high and low glucose events in the wearer by about half.
It is important to note that all the current continuous glucose monitors are approved only for use with and alongside conventional glucose meters.
This means that before acting on the information the continuous monitor provides, you should verify it by obtaining a reading with your regular monitor.
Also, the two technologies provide similar but slightly different information. The conventional monitor measures blood glucose from the blood droplet resulting from the finger prick.
The continuous meter does not use blood. Instead, it measures the glucose level in the fluid bathing the tissue under the skin.
This is in fact derived from the blood plasma itself, but it takes several minutes to adjust to reflect the blood level.
The available continuous meters need to be calibrated twice daily. (Medtronic Guardian, Dexcom 7 with a conventional fingerstick reading, although the newer Abbott Freestyle Navigator needs only four calibration readings in a 5-day period.
Once introduced, the sensor/transmitter can be worn for 3 (Guardian), 5(Navigator), or 7(Dexcom-7) days before the sensor must be changed.
The decision as to whether to get one of these monitors depends on the value to the wearer of knowing his or her readings on a minute-by-minute basis.
For people early in the course of diabetes, on oral medications, and in good control, they are probably not necessary.
For people on insulin, with a history of low and high readings, especially if they are hard to predict or explain, the information provided by continuous glucose sensing may be very valuable.
However, approval for insurance coverage is often limited to specific circumstances, such as the frequent occurrence of very high or low blood sugars that cannot otherwise be prevented.