Glucose sensors have been in use since the 1960’s in order to test the blood glucose levels in patients with diabetes mellitus. Diabetes patients who require insulin, that being all patients with Type 1 diabetes and many with Type 2, need to closely monitor their blood glucose levels to prevent them from going into either hyperglycemia (blood sugar too high) or hypoglycemia (too low). Type 1 diabetics have a defect in their pancreas that causes the pancreas to stop producing insulin, which makes insulin injections a must for Type 1 diabetics. Because of the complete lack of insulin created by their body, Type 1 diabetics will often have to test their blood glucose levels over ten times a day. On the other hand Type 2 diabetics produce insulin but it is often inefficient because of insulin resistance or some other deficiency. As their bodies actually do produce some insulin they do not have to check their blood glucose levels as often, only having to use a glucose sensor between one and four times a day. The two types of glucose sensors that are currently in use today are the blood glucose meter, which is a small handheld device which is used to manually monitor glucose levels, and the continuous glucose monitor, which is used to automatically monitor glucose levels.
- Pre-1960’s – Urine strips
- 1962 – First glucose enzyme electrode created by Leland Clark and Ann Lyons
- 1965 – First test strips using blood, called Dextrostix, developed by Ames 
- 1971 – Ames Reflectance Meter is patented 
- 1972 – Ames Eyetone Meter is patented 
- 1970’s – Design of continuous glucose monitors begin
- 1980’s – Glucometer and Accuchek sold in home market 
- 1990's-2000's - Continuous Glucose Monitors are sold in home market
Blood Glucose Meter
The blood glucose meter is the most common and one of the oldest methods of blood glucose monitoring. The first blood glucose meter was patented in 1971 by Anton H. Clemens and sold by the company Ames under the name, the Ames Reflectance Meter (AMR) . The Ames Reflectance Meter was a heavy piece of equipment, being around three pounds and had a tendency to break down, specifically in regards to the battery leaking. The Ames Reflectance Meter was followed up the following year with the Ames Eyetone Meter (AER) , which was a lighter and more effective model. Both of these two original models utilized the Dextrostix, which was also created by Ames. Both of these meters by Ames saw extended use throughout doctor’s offices, but did not see much home use because of the price, $600 for the AMR and $300 for the AER, and the various problems each had . It was not until the 1980’s when glucose meters truly became common in the home market. During this period both the Glucometer and the Accuchek were produced, both of which are the basis for the modern blood glucose meter . The device had three main parts, the lancet, the meter itself, and the test strip. The lancet is fairly simply in design, with a double edged needle-like blade with a plastic handle and a protective plastic cap. Test strips are about one inch in length and contain a glucose oxidase coating which allows the system to read the glucose levels in the blood. These meters are fairly easy to use and understand. The steps involved are:
1. Wash hands.
2. Place a clean test strip in the meter.
3. Sterilize area of finger being used with alcohol wipe.
4. Prick sterilized area with a new lancet and safely dispose.
5. Gently put pressure on finger to produce blood and place on strip.
6. Wait for reading then safely dispose of test strip.
Continuous Glucose Monitoring System
A continuous glucose monitor serves the same basic function as a blood glucose meter, in that it is designed to measure the glucose levels in the blood. The difference however is rather than manually read the blood glucose level once, a continuous glucose monitoring system automatically measured and displays the blood glucose level. A continuous glucose monitor can spit out glucose readings every 5 minutes or every minute and is capable of alerting the patient using an alarm if the blood glucose levels are either too high or too low. This makes it much more versatile than the standard blood glucose meter, which can only be used a certain number of times each day.
A continuous glucose monitor is implanted into the skin, generally in the abdomen. Thereafter the monitor can be kept in the body for up to six days before it must be replaced. However, these monitors have been found to not be as reliable or accurate as manual blood glucose meters and for that reason are not as widespread. Also, continuous glucose monitors are not covered by most health insurance providers which makes them much more difficult for most people to acquire. Because they are difficult to obtain continuous glucose monitors are used to test for trends in blood glucose levels and blood sugar levels rather to monitor blood glucose levels on a day to day basis. 
Research is currently underway on a continuous closed-loop drug delivery system that can be implanted under the skin. The idea behind this system is to be able to read the blood glucose levels and then automatically dispense insulin into the body without human assistance. They are small, approximately 1 inch in length and less than 0.25 inch in diameter. These systems are in the preliminary research stage involving animal testing and have not yet shown the ability to be viable for more than a few days. 
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