Non-invasive system for the determination of analytes in body fluids

#The present invention relates generally to systems for the determination of analytes in body fluids, and, more particularly, to a system for the non-invasive determination of analytes in body fluids.

#Those who have irregular blood glucose concentration levels are medically required to regularly self-monitor their blood glucose concentration level. An irregular blood glucose level can be brought on by a variety of reasons including illness such as diabetes. The purpose of monitoring the blood glucose concentration level is to determine the blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious implications. When blood glucose levels drop too low—a condition known as hypoglycemia—a person can become nervous, shaky, and confused. That person's judgment may become impaired and that person may eventually pass out. A person can also become very ill if their blood glucose level becomes too high—a condition known as hyperglycemia. Both conditions, hypoglycemia and hyperglycemia, are potentially life-threatening emergencies.

#Common methods for monitoring a person's blood glucose level are invasive in nature. Typically, in order to check the blood glucose level, a drop of blood is obtained from the fingertip using a lancing device. The blood drop is produced on the fingertip and the blood is harvested using the test sensor. The test sensor, which is inserted into a testing unit, is brought into contact with the blood drop. The test sensor draws the blood to the inside of the test unit which then determines the concentration of glucose in the blood.

#Other objects and advantages of the invention will become apparent upon reading the following detailed description in conjunction with the drawings in which:

#FIG. 1 is a functional block diagram of a transmission-based system for determining analytes in body fluids according to one embodiment of the present invention;

#FIG. 2 is a plot of the absorbency of transmitted light versus wavelength of the transmitted light according to one embodiment of the transmission-based system illustrated in FIG. 1;

#Referring to the drawings and initially to FIG. 1, a transmission-based noninvasive system 10 (“the system 10”) for the determination of analytes in body fluids is functionally illustrated. While the present invention will be discussed in connection with determining a patient's glucose level, the present invention is applicable in the analysis of any analyte in body fluid that exhibits spectral characteristics. Briefly, the system 10 inputs near infrared light to a piece of skin, such as the “web” of skin between a patient's index finger and thumb, and records the light transmitted through that piece of skin in order to determine the patient's glucose level. Conventionally, a patient's glucose level is referred to as a patient's blood-glucose level. However, to refer to a blood glucose level implies ignoring the amount of glucose contained in a patient's extra-cellular material and inter-cellular material. Accordingly, the inventors of the present invention prefer to refer to a patient's glucose level.

#Human skin is made of approximately fifty to sixty percent intercellular material with the balance comprising extracellular material. The extracellular material comprises approximately one-third plasma (blood) and about two-thirds interstitial fluid (“ISF”). Therefore, when examining the spectral characteristics of glucose from light that is transmitted though a patient's skin, it is important to consider glucose in that portion of skin as a whole, rather than solely the glucose in a patient's blood. The largest portion of the transmitted light is made up of light transmitted though ISF, and not blood. Conversely, in an invasive setting where a 10 μl drop of blood is obtained on a patient's finger tip, for example, the determined glucose concentration primarily represents the concentration of glucose in that patient's blood.

#The system 10 is used to obtain transmitted spectral information from a patient. For example, the system 10 is used in a test wherein the glucose concentration of the test subject is modulated to a plurality of different concentration levels. One such test is a glucose clamping test where the glucose level of the test subject is raised and lowered to various levels over the duration of the test. According to one embodiment, the glucose clamping test is designed to bring the test subject's glucose level to six plateau regions that range in concentration from 50 to 300 mg/dl. Each plateau is separated by about 50 mg/dl so that each region can be clearly differentiated. ISF and plasma samples are collected throughout the duration of the clamping test. The samples are collected every five minutes and are analyzed for glucose content. This measurement is used to adjust the infusion of glucose or insulin to maintain the glucose concentration of the plasma for about twenty-five minutes at a particular targeted plateau region. Very generally, the spectral data obtained over the course of the test are compared to the actual glucose levels (determined using invasive techniques) obtained during the test. From this data, a calibration algorithm is built to predict the actual glucose level of the patient based on the spectral characteristics of light transmitted through that patient's skin. This calibration algorithm can then be incorporated into a handheld version of the system 10 illustrated in FIG. 1.