A method for determining the presence of an analyte in a fluid is described along
with various components of an apparatus specifically designed to carry out the
method. The method involves taking a reflectance reading from one surface of an
inert porous matrix impregnated with a reagent that will interact with the analyte
to produce a light-absorbing reaction product when the fluid being analyzed is
applied to another surface and migrates through the matrix to the surface being
read. Reflectance measurements are made at two separate wavelengths in order to
eliminate interferences, and a timing circuit is triggered by an initial decrease
in reflectance by the wetting of the surface whose reflectance is being measured
by the fluid which passes through the inert matrix. Repeatability is insured by
a normalization technique performed on the light source before each reading, and
an alignment method operated on the reagent strip prior to emplacement on the apparatus.
The method and apparatus are particularly suitable for the measurement of glucose
levels in blood without requiring separation of red blood cells from serum or plasma.
