Method and apparatus for non-invasive determination of physiological chemicals, particularly glucose

Non-invasive measurements of physiological chemicals such as glucose in a test subject are made using infrared radiation and a signal processing system. The level of a selected physiological chemical in the test subject is determined in a non-invasive and quantitative manner by a method comprising the steps of: (a) irradiating a portion of the test subject with near infrared radiation; (b) collecting data concerning the irradiated light on the test subject; (c) digitally filtering the collected data to isolate a portion of the data indicative of the physiological chemical; and (d) determining the amount of physiolgocial chemical in the test subject by applying a defined mathematical model to the digitally filtered data. The collected data is in the form of either an absorbance spectrum or an interferogram.