Estimating fat in feces by near-infrared reflectance spectroscopy.

We describe use of near-infrared reflectance spectroscopy (NIRRS) to estimate the amount of fat in feces, for diagnosis of steatorrhea. After sample homogenization, the spectrum of the fecal homogenate is scanned over the near-infrared region. Assay of 94 samples of feces having a known concentration of fat showed the appropriate wavelengths for the NIRRS procedure to be 1734, 1778, 1818, 2270, and 2310 nm. The reflectance output of 47 fecal samples subsequently measured at these wavelengths was used to compute the reflectance scaling factors (F values) by the instrument's microprocessor. Assay of fat content in a further 124 fecal samples, by both hydrolysis/titration (J Biol Chem 1949;177:347) and the NIRRS procedure at the wavelengths and corresponding F values previously determined, gave results that correlated highly satisfactorily. However, the NIRRS procedure demonstrated much better precision.