Rapid and simultaneous analysis of direct and indirect bilirubin indicators in serum through reagent-free visible-near-infrared spectroscopy combined with chemometrics.

Indirect (IBil), direct (DBil) and total (TBil) bilirubin are important clinical indicators of hepatobiliary diseases, which require rapid detection in diagnosis and treatment. IBil and DBil have a structural relationship with several macromolecules in hepatobiliary metabolism. Here, the rapid analysis models for bilirubin indicators using serum visible-near-infrared (Vis-NIR) spectroscopy were established. Norris derivative filter with optimisation was used for spectral pretreatment; the optimal parameters (derivative order, number of smoothing points, number of differential gaps) were (2, 15, 9) for IBil; (2, 13, 9) for DBil, respectively. Equidistant combination-partial least squares (EC-PLS) was used for large-scale wavelength screening. Wavelength step-by-step phase-out PLS (WSP-PLS) was used for secondary wavelength optimisation. The wavelength models of the optimal EC-WSP-PLS for IBil and DBil included 11 and 18 wavelengths, respectively. In independent validation, the root-mean-square errors and correlation coefficient for prediction (SEP, R), and ratio of performance-to-deviation (RPD) were 0.90 μmol L, 0.975, and 4.4 for IBil; 0.71 μmol L, 0.955, and 3.3 for DBil, respectively. TBil was subjected to spectral analysis, and the summation of the prediction values of IBil and DBil was compared. The latter was obviously better, and SEP, R, RPD were 0.82 μmol L, 0.990, 7.1, respectively. The results for IBil, DBil and TBil indicated high correlation, low error and good overall prediction ability and confirmed the feasibility of the simultaneous analysis of bilirubin indicators through reagent-free serum Vis-NIR spectroscopy. The proposed method is crucial for the rapid screening of large populations and the treatment of hepatobiliary diseases.