Correlations between the serum bilirubin level and ulcerative colitis: a case–control study

Objective To analyze whether the bilirubin level is a protective factor in ulcerative colitis (UC) and the predictive value of the bilirubin level. Patients and methods We compared the bilirubin levels of 100 UC patients and 140 healthy controls as well as those of the subgroups of patients with different UC severities and then analyzed the correlation between the bilirubin level and UC and the correlations among the erythrocyte sedimentation rate (ESR), high sensitivity C-reactive protein (hs-CRP) level, UC severity, and bilirubin level. The predictive value of the bilirubin level for UC was determined by constructing a receiver operating characteristic (ROC) curve. Results The mean levels of the total bilirubin (TBIL) and indirect bilirubin (IBIL) in the UC were lower in comparison with the mean TBIL and IBIL levels in the control group, and the TBIL and IBIL levels were significantly higher in the mild activity subgroup than in the moderate and severe activity subgroups ( P <0.05). TBIL ( P <0.001, 95% confidence interval: 0.794–0.918) and especially IBIL ( P <0.001, 95% confidence interval: 0.646–0.809) were independent protective factors for UC. There were also significant differences in the serum ESR and hs-CRP levels between the patients with different UC severities (ESR= χ 2 : 23.975; hs-CRP= χ 2 : 26.626, P <0.001), and there was a positive correlation between these two parameters (ESR= r : 0.472; hs-CRP= r : 0.495, P <0.001). However, the TBIL and IBIL levels were correlated negatively with the ESR ( r total =−0.429, r indirect =−0.461, P <0.001) and hs-CRP ( r total =−0.289, r indirect =−0.25, P <0.05) levels. The ROC curve showed that the threshold values of TBIL and IBIL were 8.87 and 6.735 µmol/l, the areas under the maximum ROC curve were 0.664 and 0.716, the sensitivities were 0.450 and 0.61, and the specificities were 0.800 and 0.786, respectively. Conclusion TBIL and especially IBIL may be independent protective factors for UC because of their antioxidant and anti-inflammatory effects. A low level of IBIL has a moderate predictive value for UC, and an IBIL level less than 6.735 µmol/l can be used as a defining index for predicting UC.