Correlation of Serum Bilirubin with Clinical and Pathological Characteristics of Patients with IgA Nephropathy.

Objective: To investigate the correlations of total bilirubin (TBIL), direct bilirubin (DBIL), and indirect bilirubin (IBIL) with various clinical indicators and pathological features of patients with IgA nephropathy (IgAN).

Methods: Patients diagnosed with IgAN were included and divided into low and high TBIL/DBIL/IBIL groups. Correlation analysis was performed to assess the relationships between the bilirubin indices and other clinical and pathological variables. Logistic regression was applied to identify the independent risk factors of mesangial cell proliferation (corresponding to M1 in the Oxford classification of IgAN).

Results: Totally 192 patients with IgAN were included, and the patient clinical indicators were compared between the different bilirubin subgroups. Compared to the groups with higher TBIL, DBIL, and IBIL levels, groups with lower values of these bilirubin indices exhibited a higher 24-hour urine protein (24hUP) concentration but a lower proportion of males as well as reduced total protein, albumin, haemoglobin, and glutamic-pyruvic transaminase levels (p < 0.05). Moreover, the low-DBIL group displayed higher total cholesterol, triglyceride, and low-density lipoprotein (LDL) concentrations (p < 0.05) than those in the high DBIL group. Spearman analysis further revealed that TBIL, DBIL, and IBIL were negatively correlated with 24hUP and positively correlated with haemoglobin, total protein, and albumin (p < 0.05). Additionally, DBIL exhibited negative correlations with total cholesterol, triglyceride, and LDL (p < 0.05). From a pathological perspective, M1 incidence was higher in the low TBIL and IBIL groups (both p < 0.05). Furthermore, the high IBIL group showed a lower occurrence of cellular/fibrocellular crescents (C1 (in at least one glomerulus) and C2 (in >25% of glomeruli) in the Oxford classification, p < 0.05). Lastly, the multivariate regression model suggested that IBIL was an independent protective factor for M1 (odds ratio = 0.563, 95% confidence interval = 0.344-0.921, p = 0.022).

Conclusions: Patients with IgAN accompanied by low values of bilirubin indices exhibit worsened disease-related clinical indicators (24hUP, total protein, albumin, and haemoglobin levels). Reduced TBIL and IBIL concentrations are indicative of severe renal pathology, with IBIL being a protective factor against M1.