Noninvasive Glucose Measurement

Barbara Deschamp, Timothy Ficarra, Eric Murray

Abstract:

Diabetes mellitus is a metabolic disease that affects over 25 million people in the United States. Those with the disease need to be have constant awareness of their blood glucose levels, or can suffer severe consequences. In this paper, we discuss the current methods used by diabetics for blood glucose measurement, and explore the current implementations of noninvasive glucometry strategies in order to make a prediction as to which measurement techniques may eventually replace today's blood sampling methods.

1. Introduction

People with diabetes are tasked with monitoring their blood glucose levels throughout the day to ensure that these levels remain in a healthy range. Because this measurement is so crucial to their health, it is important that people can take it safely and easily. The most popular method for measuring the glucose content of blood is to obtain a blood sample and apply it to a glucometer. As a result, millions of people are forced to prick the skin in their fingers many times a day in order to draw blood. However, scientists and engineers have been working on many different approaches to eliminate this inconvenience by way of noninvasive glucose monitors: sensors that can obtain an accurate reading of blood glucose levels without the need for a blood sample.

The rest of the paper is outlines as follows. Section 2 provides an overview of what diabetes is and how it affects people. Section 3 discusses the invasive glucose measurement strategies currently in use today. In Section 4, the different strategies for noninvasive glucose measurement are discussed. Finally, Section 5 gives the main conclusions regarded the feasibility of the methods described in Section 4 are presented.

2. Overview of Diabetes

Diabetes is an autoimmune disease that results from the pancreas losing its ability to provide the quantity or quality of insulin needed to break down glucose. When carbohydrates enter the digestive system, they are broken down into glucose that is normally utilized by the cells for energy. However, insulin is needed for the cells to actually use that glucose. If the pancreas cannot produce the necessary amount of insulin, excess glucose will build up in the blood stream, causing major consequences.

Two types of diabetes exist. Type I, Insulin Dependent Diabetes Mellitus, accounts for 5-10% of cases. It usually occurs in childhood as a result of a genetic predisposition and an environmental trigger (although that trigger is not yet known). The pancreas loses its ability to produce insulin, so diabetics need to directly inject insulin into their bloodstream. Type II, Non-Insulin Dependent, generally occurs later in life, as a result of obesity and other factors. In this case, the pancreas is still functioning, but it cannot meet the body's demands for insulin. Therefore, insulin is taken orally. In some cases, Type II diabetes is curable with weight loss, diet, and exercise.

If a person's blood sugar is left unregulated, it can lead to a multitude of complications over time. The combination of the inability to utilize the glucose in the body and the extra work required to remove the excess glucose can damage many organ. Among these are the eyes, the kidneys, and the heart. Furthermore, peripheral neuropathy, or nerve damage, can occur all over the body which can result in amputation. Also, a diabetic has a greater risk of stroke [1].

Diabetes has a profound presence. There are current 25.8 million people in the United States with diabetes, which accounts for 8.3% of the country's population [1]. An estimated 7 million people have diabetes but are undiagnosed. In 2010 alone, 1.9 million new cases of diabetes were diagnosed in people over the age of 20. Furthermore, childhood Type II diabetes is at an all time high, as it is directly linked to childhood obesity.

Along with the large number of people affected by diabetes are the large health care costs. In 2007, $174 billion was spent treating diagnosed diabetes [1]. $116 billion of that was for direct medical costs, while another $58 billion was for disability and work loss costs. Minimizing the costs of diabetes-related health care requires the prevention of major complications through by controlling blood sugar levels. If a diabetic can maintain his or her blood glucose levels with accurate measurement and treatment then the risks of complications goes down significantly. Therefore, reliable glucose measurement methods are needed to keep people healthy and keep health care costs low.

3. Invasive Glucose Measurement

Currently there are two main methods of measuring blood glucose levels. The first is called the A1C test. A1C is a simple lab test where a small amount of blood is drawn for analysis. The objective is to determine the average glucose level in a patient over the last three months. These results are an indication of a person's risk for the medical complications described in Section 2, and are presently the best way of monitoring a diabetic's health over a long term basis. For diabetics, an A1C test is recommended at least twice a year. Table 1 shows the relationship between the A1C level and average glucose level. Although the A1C test is an important indicator of long-term health, diabetics also need to conduct frequent self tests.

Table 1. A1C Testing Relationship [2].

A1C Level / Average Glucose Level
12 / 345
11 / 310
10 / 275
9 / 240
8 / 205
7 / 170
6 / 135

Diabetics perform self tests for blood glucose levels on a daily or even hourly basis. These tests reveal the current amount of glucose present in the blood, so that immediate action can be taken if necessary. First, the person pricks his or her finger with a lancet to extract a drop of blood. Next, that blook is placed onto a strip containing glucose sensitive chemicals. An optical meter then analyzes this sample to provide a numerical reading of the blood glucose level. Depending on the sensor in use, either the plasma or the whole blood content is used for the sample. For a plasma sensor, a value of 90-130 mg/dL is healthy before meals, with a value of less than 180 mg/dL 1 to 2 hours after meals. Comparatively, for a whole blood value glucometer, 80-120 mg/dL and 170 mg/dL are expected before and after a meal, respectively [3].

Other self test methods that exist include meters that use alternative site tests, such as upper arms and forearm, although these are not a replacement for finger pricks. Another method involves using a Laser to draw blood which was approved by the FDA in 1998. There is also an invasive continuous monitoring system that exists: The MiniMed monitoring system [4]. This device involves works by inserting a small plastic catheter under the skin to continually take readings and even inject insulin automatically.

The concern with these testing methods is that they cause discomfort to those who have to administer them on a regular basis. The blood sampling methodsare an even greater challenge for people prone to having Vasovagal episodes and fainting at the sight of blood. For this reason, many scientists are looking for a noninvasive alternative, measuring blood glucose levels without direct contact with blood.

4. Noninvasive Glucose Measurement Strategies

Ideally, diabetics want a noninvasive measurement technique which produces no pain or discomfort, involves no blood or other bodily fluid obtained by piercing the skin, and does not cause tissue damage, injury, or deterioration. Despite many attempts by several universities and manufacturers, no such product has yet to exist. However, many different strategies are being tested now, including reverse iontophoresis and spectroscopy.

Reverse iontophoresis is the process of removing molecules from within the body for testing purposes, by means of a small electrical charge. In this case, the removal of glucose through the skin is done with an electrical field. The field attracts sodium ions with water and glucose. The first consumer device utilizing this method was the GlucoWatch in 2002. The GlucoWatch is worn like a watch and monitors blood glucose level via tiny electric currents. While the GlucoWatch is a noninvasive measurement tool, it has several flaws. A report by the FDA states that half of all users experience skin irritation [5]. Furthermore, in clinical studies, the GlucoWatch was shown to produce readingsthat were offmore than 30% off, 25% of the time. To clarify, one out of every four tests would be erroneous by up to 30%. These inaccurate results were more common when blood glucose levels were below normal. Therefore, the GlucoWatch failed to be a reliable replacement for the invasive finger-pricking method.

Another field of research in noninvasive glucose measurement is spectroscopy, the study of the interaction of matter in light. Usually a beam of light is focused on some area of the body. Depending on what substances are present, the light will react in different ways. The change in light characteristics are then measured and interpreted. This method can be broken down into three different subcategories: Near infrared spectroscopy, photoacoustic spectroscopy, and scatter changes.

Near infrared spectroscopy functions in the .7 – 2.5 micrometer range of the light spectrum. It explores tissue depths of 1 to 100 millimeters. The inner-lip is an example of a viable region for near infrared spectroscopy. Compared to a traditional blood test, these results suffer a ten minute delay [6].

Photoacoustic spectroscopy is when a beam of light rapidly heats a target. This beam generates an acoustic pressure wave which is measured by a microphone. While accurate glucose readings are possible with this method, the equipment is expensive and sensitive to environmental changes [6].

Scatter changes involves the refractive index of a sample. Specifically, the increase in the presence of glucose in a sample will increase the sample's refractive index. Measuring light refraction against the abdomen has been found to be a very accurate indicator of blood glucose levels. The problem with scatter change methods is that calibrating a baseline, which is the normal refraction index of the sample, is very difficult. The process also needs to account for signal shift due to environmental factors [6].

The glucose measurement strategies listed here are only a few of the possible techniques that are currently being researched. For our future papers, the methods described here will be elaborated on, and numerous other methods will be examined.

5. Conclusion

Over the next few weeks, we intend to dive deeper into the noninvasive glucose measurement strategies that exist. Each of the three of us will investigate different methods and see the results researchers have come up with. Each week we'll each explore a given strategy, see which universities have conducted research on them, and what their results were. The information we collect will be used to make a prediction about which glucometry methods will eventually replace the invasive procedures of today. Our written time line for work is given below.

3/01 - 4/05 :

  • Tim will look into the feasibility of reverse iontophoresis, what research has been done, and what results there have been.
  • Eric will continue to look into various types of spectroscopy and determine which will most likely be on the market in the future.
  • Barbara will look into the most recent other methods that have not been listed here and determine what has been done and what is currently being researched.

4/05 – 4/26:

  • During this time we will work together and write our paper, discussing which method we most likely think will succeed and how it will progress into the market. If necessary, we will also expand on the depth of information for the noninvasive glucose measurement strategies given in the previously submitted paper.

5/03

  • Written paper will be submitted to the Journal of Diabetes Science and Technology.

6. References

[1]"Diabetes Statistics - American Diabetes Association." 26 Jan. 2011. Web. 28 Feb. 2011.

[2] Mathur, Ruchi. "Hemoglobin A1c Test Information on MedicineNet.com." MedicineNet. Ed. William C. Shiel. 15 Jan. 2009. Web. 01 Mar. 2011. <

[3] "Diabetes - What Should My Blood Sugar Levels Be? - Diabetes Mellitus, Type 2 Diabetes, Type 1, and Metabolic Disorders Treatment and Medications on MedicineNet.com." MedicineNet. Ed. William C. Shiel. 29 Mar. 2002. Web. 01 Mar. 2011.

[4] "Product Information." Medtronic Minimed, Inc. Web. 01 Mar. 2011.

[5] Mendosa, David. "GlucoWatch." David Mendosa: A Writer About Diabetes. 31 Oct. 2007. Web.

01 Mar. 2011. <

[6] Waynant, R. W., and V. M. Chenault. "Overview of Non-Invasive Optical Glucose Monitoring Techniques." IEEE - The World's Largest Professional Association for the Advancement of Technology. Apr. 1998. Web. 01 Mar. 2011. <