A system and method for determining the concentration of analytes of interest in complex matrices is provided. According to one aspect of the present invention, near-infrared analytical radiation is generally directed onto a portion of a specimen containing the analyte of interest. A wavelength of the analytical radiation is scanned over the specimen over a broad range of frequencies and over a short duration of diagnostic time. A spectrum of radiation is transmitted through, reflected from or scattered from the specimen and collected by a detector. The concentration of the analyte of interest in the specimen is determined by the radiation collected by the detector.