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Blood Glucose Monitoring
Blood glucose monitoring is a way of testing how much glucose is in the blood (glycemia). This is important in the care of diabetes mellitus. Most people with Type 2 diabetes need to test at least once per day (usually before breakfast) to assess the effectiveness of their diet and exercise for controlling their blood glucose levels. Many people with Type 2 are using an oral medication to combat their insulin resistance, and must test their blood glucose before and after breakfast to assess the effectiveness of their dosage. All people who need to inject insulin, both for Type 1 diabetes and Type 2, need also to test their blood sugar more often (3 to 10 times per day) to assess the effectiveness of their prior insulin dose and to calculate their next insulin dose.
Improved technology for measuring blood glucose is rapidly changing the standards of care for all diabetic people. There are several methods of blood glucose testing currently available.
Chemical Test Strips
Chemical test strips are a low cost method for monitoring blood glucose. A fairly large drop of blood, usually taken from the fingertip, is placed on a chemically prepared strip, called a blood glucose testing strip. The strip chemistry will cause it to change color according to the amount of glucose is in the blood. One can tell if their level of blood glucose is low, high, or normal by comparing the color on the end of the strip to a color chart that is printed on the side of the test strip container.
These are recommended only for people who are occasionally monitoring their blood glucose level (prediabetic or Type 2) and are not using insulin.
Blood Glucose Meters (Glucose Readers or Glucometers)
Four generations of blood glucose meter, c. 1993-2005. Sample sizes vary from 30 to 0.3 Âµl. Test times vary from 5 seconds to 2 minutes (modern meters are typically below 15 seconds). A blood glucose meter or reader is an electronic device for measuring or reading the blood glucose level. A relatively small drop of blood is placed on a disposable test strip which interfaces with a digital meter. Within several seconds, the level of blood glucose will be shown on the digital display.
While more expensive, blood glucose meters seem a breakthrough in diabetes self care. As the drops of blood needed for the meter become smaller, the pain associated with testing is reduced and the compliance of diabetic people to their testing regimens is improved. Although the cost of using blood glucose meters seems high, it is believed to be a cost benefit relative to the avoided medical costs of the complications of diabetes.
A recent and welcome advance is the use of small blood drops for blood glucose testing from other places than the finger tips. This alternate site testing uses the same test strips and meter, is practically pain free, and gives the real estate on the finger tips a needed break if they become sore.
Continuous Blood Glucose Monitoring
A continuous blood glucose monitor determines blood glucose levels on a continuous basis (every few minutes). A typical system consists of:
Continuous blood glucose monitors measure the glucose level of interstitial fluid. Disadvantages compared to traditional blood glucose monitoring are:
The lag time discussed above has been reported to be about 5 minutes. Anecdotally, some users of the various systems report lag times of up to 10-15 minutes. This lag time is insignificant when blood sugar levels are relatively consistent. However, blood sugar levels, when changing rapidly, may read in the normal range on a CGM system while in reality the patient is already experiencing symptoms of an out-of-range blood glucose value and may require treatment. Patients using CGM are therefore advised to consider both the absolute value of the blood glucose level given by the system as well as any trend in the blood glucose levels. For example, a patient using CGM with a blood glucose of 100 mg/dl on their CGM system might take no action if their blood glucose has been consistent for several readings, while a patient with the same blood glucose level but whose blood glucose has been dropping steeply in a short period of time might be advised to perform a fingerstick test to check for hypoglycemia.
Continuous monitoring allows examination of how the blood glucose level reacts to insulin, exercise, food, and other factors. The additional data can be useful for setting correct insulin dosing ratios for food intake and correction of hyperglycemia. Monitoring during periods when blood glucose levels are not typically checked (e.g. overnight) can help to identify problems in insulin dosing (such as basal levels for insulin pump users or long-acting insulin levels for patients taking injections). Monitors may also be equipped with alarms to alert patients of hyperglycemia or hypoglycemia so that a patient can take corrective action(s) (after fingerstick testing, if necessary) even in cases where they do not feel symptoms of either condition. While the technology has its limitations, studies have demonstrated that patients with continuous sensors experience less hyperglycemia and also reduce their glycated hemoglobin levels.
Currently, continuous blood glucose monitoring is not automatically covered by health insurance in the United States in the same way that most other diabetic supplies are covered (e.g. standard glucose testing supplies, insulin, and even insulin pumps). However, an increasing number of insurance companies do cover continuous glucose monitoring supplies (both the receiver and disposable sensors) on a case-by-case basis if the patient and doctor show a specific need. The lack of insurance coverage is exacerbated by the fact that disposable sensors must be frequently replaced (sensors by Dexcom and Minimed have been FDA approved for 7- and 3-day use, respectively, though some patients wear sensors for longer than the recommended period) and the receiving meters likewise have finite lifetimes (less than 2 years and as little as 6 months). This is one factor in the slow uptake in the use of sensors that have been marketed in the United States.
Some current and future continuous glucose monitoring products include:
This technology is an important component in the effort to develop a closed-loop system connecting real-time automatic control of an insulin pump based on immediate blood glucose data from the sensor. One important goal is to develop an algorithm for automatic control, by which the system would function as an artificial pancreas. However, this is a long-term goal at this point for companies that manufacture such systems, as such an algorithm would need to be very complex in order to accurately control blood sugar levels without any user input.
Glucose sensing bio-implants
Longer term solutions to continuous monitoring, not yet available but under development, use a long-lasting bio-implant. These systems promise to ease the burden of blood glucose monitoring for their users, but at the trade off of a minor surgical implantation of the sensor that lasts from one year to more than five years depending on the product selected.
Products under development include:
Some new technologies to monitor blood glucose levels will not require access to blood to read the glucose level. Non-invasive technologies include near IR detection, ultrasound and dielectric spectroscopy. These will free the person with diabetes from finger sticks to supply the drop of blood for blood glucose analysis.
Most of the non-invasive methods under development are continuous glucose monitoring methods and offer the advantage of providing additional information to the subject between the conventional finger stick, blood glucose measurements and over time periods where no finger stick measurements are available (i.e. while the subject is sleeping).
Products under development include:
For patients with diabetes mellitus Type 2, the importance of monitoring and the optimal frequency of monitoring are not clear. One randomized controlled trial found that self-monitoring of blood glucose did not improve the Hba1c among "reasonably well controlled non-insulin treated patients with Type 2 diabetes".
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