The present invention provides a method for measuring a blood analyte
concentration of a body part comprising removing a portion or all of the
blood from the body part to produce a modified body part, and recording a
first absorbance value of the modified body part. This is followed by
filling the body part with blood to produce a filled body part, and
recording a second absorbance value of the filled body part. A difference
spectrum is obtained by subtracting the first absorbance values from the
second absorbance values, and a calibration algorithm for the blood
analyte is applied to the difference spectrum, thereby measuring the
concentration of the blood analyte. Also provided is an apparatus for
determining the concentration of a blood analyte of a body part. The
apparatus comprising a chamber of a size and shape to receive the body
part, where the chamber comprises an element for withdrawing and
reintroducing blood from the body part, when the body part is inserted
within the chamber. The chamber also comprising one or more than one port
for introducing electromagnetic radiation into the chamber and onto that
body part, and collecting remaining electromagnetic radiation following
interaction with the body part.