Patent ID: 6844195

Claim:
A method for determining whether blood in a stool came from an upper gastrointestinal site or a lower gastrointestinal site, comprising the steps of: (a) collecting a stool sample containing hemoglobin and/or iron heme compounds derived from hemoglobin in its ferrous state and/or its ferric state and preparing the stool sample at a predetermined pH for analysis by spectroscopy; (b) measuring an absorption spectrum of the stool sample at the predetermined pH using a spectrophotometer calibrated relative to a first absorption spectrum with a first Soret absorption peak approximately centered at a first wavelength of about 415 nanometers for pure ferrous heme at the predetermined pH and a second absorption spectrum with a second Soret absorption peak approximately centered at a second wavelength of about 408 nanometers for pure ferric heme at the predetermined pH; and (c) determining whether the blood in the stool came from the upper gastrointestinal site or the lower gastrointestinal site based on an analysis of the stool sample absorption spectrum by determining that the blood in the stool sample has passed through stomach acid and therefore came from the upper gastrointestinal tract if an absorption peak of a main Soret band of the stool sample absorption spectrum is closer to the second wavelength of about 408 nanometers than to the first wavelength of about 415 nanometers, or that the blood in the stool sample has not passed through stomach acid and therefore came from the lower gastrointestinal tract if an absorption peak of the Soret band of the stool sample absorption spectra is closer to the first wavelength of about 415 nanometers than to the second wavelength of about 408 nanometers.