History
Home blood glucose testing started in the mid-1970's. It quickly became apparent that patients were capable of monitoring their blood sugars at home, with improvement in the Hemoglobin A1C. Of course, in those days there was no proof that improving glycemic control improved outcomes. In fact, the pioneers of home blood glucose testing had to wait almost twenty years to find out that their efforts were worthwhile.
The first home glucose monitor, the reflomat, was a desktop reflectance meter designed to read the color changes on the Boeringher-Manneheim Chemstrip BG. We had one of these monitors in our home in 1978. Hoping that the complications of diabetes were related to high blood sugar levels, and not to some underlying genetic or autoimmune problem, Val began to measure her blood sugar level several times a day. This was a vast improvement over the monthly monitoring done at the local hospital.
Of course, today's glucose monitors are smaller, faster, cheaper, and more accurate. While there have been vast improvements in the technology of home glucose monitoring, all meters continue to be based on the glucose oxidase sysem, which is the same system used by the pancreas to measure blood sugars.
The Evolution of Home Glucose Monitors
Several years ago efforts were made to determine the blood glucose by near infra-red spectrophotometry, the so-called "dream beam". The idea was to determine the blood glucose level by ascertaining the transmission of a beam of light transmitted through the finger. Val participated in this research, both at the NIH (National Istitutes of Health), and by submitting data from a meter we had in our home. Since the oxygen level in the blood is accurately measured using this technology, there was reason to believe that the blood glucose level could also be accurately measured. Unfortunately, this technology did not pan out. Val's measured blood sugars regularly ran from minus 700 to over 1000.
The next major improvement came with the FDA approval of Minimed's Continuous Glucose Monitoring System (CGMS). With this system, blood sugars could be measured every 5 minutes, 24 hours a day, for up to 3 days. While the earliest models did provide much useful information, it was not nearly as accurate as traditional home glucose monitoring. Also, the user could not read the actual blood glucose level in real time. Only after the data was downloaded by the physician could the results be viewed and analyzed. While not FDA approved, we set the meter to "signal" mode so that we could view the signal strength in real time. Fluctuations in signal strength prompted Val to do a finger stick blood sugar analysis.
The latest iteration of Minimed's CGMS is the Guardian RT. This system displays the blood sugar level and alarms when the glucose level is above or below pre-set targets. Before any action is taken by the patient, the Guardian RT result must be confirmed by a finger stick analysis.
The Glucowatch initially showed promise as a continuous blood glucose analyzer for daily use. The watch passes a weak electric current through the skin, which causes tiny amounts of tissue fluid to seep through the skin. The underside of the watch analyzes this fluid, and the patient reads the results on the watch face. Unfortunately, the Glucowatch commonly causes significant skin irritation, limiting its utility.
With improvements in accuracy and reliability, it is hoped that the next generation of CGMS will be able to communicate directly with an insulin pump. This creates a closed loop system, enabling patients to maintain near normal blood sugars.
Practical Matters
Never share finger stick devices. The Center for Disease Control has reported that hepatitis B has been transmitted by the miniscule amounts of blood that may remain on the template, even if the needle is changed.
The ability to perceive high blood sugars and low blood sugars changes with time. Do not rely on perception alone to make therapeutic decisions, such as eating or taking more insulin. If in doubt, check your blood sugar.
Finger stick blood sugars measure the amount of glucose in the blood, NOT the tissues. Usually these numbers are almost the same. However, if your blood sugar is rising or falling very rapidly, it may take up to 10 minutes for the blood sugar to reflect the actual tissue glucose (E. Moberg, et.al.).This may be important when hypoglycemia develops rapidly. In this circumstance both the treatment and monitoring of the hypoglycemia must be followed especially carefully.
Forearm blood glucose testing is usually less painful, and correlates closely with finger stick analysis, unless the blood sugar is fluctuating rapidly. In this circumstance the finger stick blood sugar always leads forearms in the detection of blood glucose changes. In cases of hypoglycemia, or hypoglycemia unawareness, finger stick analysis should be used Kara Johnson, et. al..
After many years of finger sticks, the sides of the fingers become callused. Don't be tempted to use the fingertip pads for finger sticks. While it may be easier to obtain blood from the pads, sensation will be diminished.