Background   Different stages of chronic kidney disease (CKD) is closely associated with its treatment and prognosis, but few studies have explored the changes of renal injury indices in different CKD stages.

  Objective   To investigate the expression levels of urine α₁-microglobulin (α₁-MG), serum β₂-microglobulin (β₂-MG), cystatin C (CysC), blood urea nitrogen (BUN), and serum creatinine (SCr) in different CKD stages of IgA nephropathy.

  Methods  From October 2019 to October 2020, 120 CKD patients who were diangosed with IgA nephropathy based on pathological results in the department of nephrology, the First Medical Center of Chinese PLA General Hospital, were enrolled as case group, and according to the CKD stage, they were further divided into G1, G2, G3, G4, and G5 subgroups, with 20 patients in each subgroup. Another 40 healthy individuals were enrolled as healthy control group. The levels of α₁-MG, β₂-MG, CysC, BUN, and SCr were measured for each group, and the correlation of each index with CKD stage (estimated glomerular filtration rate eGFR) was analyzed for the case group.

  Results   In the case group, there were 68 male patients and 52 female patients, with a mean age of 47.3±15.2 years (range 21-78 years), and in the control group, there were 22 male individuals and 18 female individuals, with a mean age of 43.5±15.8 years (range 24-77 years). There were no significant differences in sex composition and age composition between the two groups (P＞0.05). All subgroups of the case group had a significantly higher level of urine α₁-MG than the control group (P＜0.05), and comparison between subgroups showed that the G5 subgroup had a significant increase than the G4 group (P＜0.05). All subgroups of the case group had a significantly higher serum level of β₂-MG than the control group (P＜0.05), and comparison between subgroups showed that the G3a, G3b, G4, and G5 subgroup had a significantly higher level than the G2, G3a, G3b, and G4 subgroups, respectively (all P＜0.01). All subgroups of the case group had a significantly higher level of CysC than the control group (P＜0.05), and comparison between subgroups showed that the G2, G3a, G3b, G4, and G5 subgroups had a significantly higher level than the G1, G2, G3a, G3b, and G4 subgroups, respectively (all P＜0.01). The G2, G3, G4, and G5 subgroups of the case group had significantly higher levels of BUN and SCr than the control group (P＜0.05), and comparison between subgroups showed that the G2, G3a, G3b, G4, and G5 subgroups were significantly higher than the G1, G2, G3a, G3b, and G4 subgroups, respectively (all P＜0.01). Pearson correlation analysis showed that urine α₁-MG, serum β₂-MG, CysC, BUN, and SCr were negatively correlated with eGFR (r = -0.611, -0.651, -0.722, -0.717, and -0.679, all P＜0.05).

  Conclusion   During the progression of CKD, urine α₁-MG, serum β₂-MG, CysC, BUN, and SCr can be used as the evaluation indices for disease progression and treatment, especially CysC, which shows a significant difference between stages and is thus the most ideal index among the five indices. It is reasonable to classify stage G3 into stages G3a and G3b in the new staging system.