New method for faecal fat determination by mid-infrared spectroscopy, using a transmission cell: an improvement in standardization

Current techniques used in clinical laboratories for faecal fat determinati on, such as the Van de Kamer method, are not very accurate or precise. This became apparent when results obtained by different laboratories were compa red, and could explain the disappointing performance of near-infrared and m id-infrared spectroscopy since the accuracy of these techniques depends upo n the accuracy of the calibration used (i.e. inaccurate wet chemical analys is). In order to improve standardization, we developed and tested a new qua ntitative method in three laboratories, based on Fourier transform infrared (FT-IR) spectroscopy. Fatty acids were extracted from faecal samples with acidified petroleum ether-ethanol and the extracts were dried and dissolved in chloroform. An infrared spectrum of the extracts was recorded in the ra nge 4000-650 cm(-1), using an infrared transmission cell. Standard mixtures of stearic and palmitic acids (65:35) were used for calibration. Quantific ation was based on the absorbance band of the CH2 group (2855 cm(-1)) of fr ee fatty acids and fatty acid glycerol esters. The calibration curve showed excellent linearity. The correlation coefficient between the titrimetric V an de Kamer and FT-IR methods was 0.96 (y = 1.12x-0.02, standard error of p rediction = 0.89 g% fat). No significant difference was found when the FT-I R results of 28 faecal samples from patients were compared between two diff erent university hospital laboratories. The new FT-IR method, using primary standards, is simple and rapid, and provides satisfactory intra- and inter -laboratory precision for the diagnosis and monitoring of steatorrhoea.