Analysis of cholyglycine acid as a biomarker for the early diagnosis of liver disease by fluorescence polarization immunoassay

•A rapid, convenient, and homogeneous fluorescence polarization immunoassay (FPIA) was developed for determination of cholyglycine concentrations.•High sensitivity with the quantification limit as low as 50.9ng/mL for cholyglycine.•Concentrations of cholyglycine in patients were much higher than those in controls and cholyglycine may be a good biomarker for the diagnosis of liver diseases. Trace concentrations of cholyglycine acid (CG) are useful to reflect the damage degree in liver cells, and useful in the diagnosis and prognosis of liver diseases. Therefore, developing an effective strategy to detect the concentration of CG is of great importance. A homogeneous fluorescence polarization immunoassay (FPIA) was developed for determination of CG concentrations. The effects of tracer concentration, antibody dilution and incubation time on FPIA performance were studied. The FPIA was used to detect CG in sera from 522 patients with liver diseases and 449 healthy controls. The results were compared with those obtained through enzyme multiplied immunoassay technique (EMIT). The FPIA showed a detection limit of 50.9ng/mL for CG and the cross-reactivity of antibodies with nine structurally and functionally related analogs were negligible. Concentrations of CG in patients with chronic hepatitis B virus, liver cirrhosis and decompensated cirrhosis were 5.4, 7.9 and 6.5-fold higher than those in controls, respectively, and hence were significantly different from controls (P