Correlation of bilirubin and toxic bile acids in critically ill patients with cholestatic liver dysfunction and adsorber application

Bilirubin is one of the most frequently used laboratory values to monitor critically ill patients with cholestatic liver dysfunction. Besides bilirubin, toxic bile acids (TBAs), which may cause severe organ damage, are typically elevated. A correlation between both parameters seems plausible, but data are lacking. The aim was to investigate whether there is a correlation between bilirubin and TBAs in patients’ blood and whether a compareable reduction can be observed during the use of the adsorber CytoSorb (CS). As part of the Cyto-SOLVE study (NCT04913298), 16 critically ill patients with cholestatic liver dysfunction, bilirubin concentration > 10 mg/dl, continuous kidney replacement therapy and CS-application were investigated. Bilirubin and TBA concentrations were measured from arterial blood at defined time points (before start, after 6 and 12 h). Relative reduction (RR) was calculated using the formula \(\:\:{\boldsymbol{RR}}\:{\boldsymbol{\left(\%\right)}}=\frac{{\boldsymbol{concentration\left(pre-post\right)}}}{{\boldsymbol{concentration\left(pre\right)}}}*{\boldsymbol{100}}\) . A moderate to high correlation between bilirubin and TBA concentration at all defined timepoints (r_start=0.64, p = 0.008; r_6h = 0.85, p < 0.001, r_12h = 0.72, p = 0.002) was observed. In the first six hours of CS-application, a significant elimination of TBA (median TBA: 30.8→20.1µmol/l, p < 0.001) and bilirubin (median bilirubin: 17.1→11.9 mg/dl, p < 0.001) was observed. The median RR after 6 h was 26.1% and 39.8% for bilirubin and TBA, respectively. No further reduction was observed after 12 h (RR_bilirubin: – 0.6%, RR_TBA: 1.8%). There was an at least moderate correlation between bilirubin and TBA in patients with cholestatic liver dysfunction. Therefore, bilirubin seems to be a suitable surrogate parameter for TBA elimination during CytoSorb application.