Objective:Rejection remains the most important factor limiting the survival of transplanted kidneys.Although a pathological biopsy of the transplanted kidney is the gold standard for diagnosing rejection,its limitations prevent it from being used as a routine monitoring method.Recently,peripheral blood lymphocyte subpopulation testing has become an important means of assessing the body's immune system,however,its application value and strategy in the field of kidney transplantation need further exploration.Additionally,the development and utilization of routine test parameters are also important methods for exploring diagnostic strategies and predictive models for kidney transplant diseases.This study aims to explore the correlation between peripheral blood lymphocyte subpopulations and T cell-mediated rejection(TCMR)and antibody-mediated rejection(ABMR),as well as their diagnostic value,in conjunction with routine blood tests. Methods:A total of 154 kidney transplant recipients,who met the inclusion and exclusion criteria and were treated at the Second Xiangya Hospital of Central South University from January to December,2021,were selected as the study subjects.They were assigned into a stable group,a TCMR group,and an ABMR group,based on the occurrence and type of rejection.The basic and clinical data of these recipients were retrospectively analyzed and compared among the 3 groups.The transplant kidney function,routine blood tests,and peripheral blood lymphocyte subpopulation data of the TCMR group and the ABMR group before rejection treatment were compared with those of the stable group. Results:The stable,TCMR group,and ABMR group showed no statistically significant differences in immunosuppressive maintenance regimens or sources of transplanted kidneys(all P>0.05).However,the post-transplant duration was significantly longer in the ABMR group compared with the stable group(P<0.001)and the TCMR group(P<0.05).Regarding kidney function,serum creatinine levels in the ABMR group were higher than in the stable group and the TCMR group(both P<0.01),with the TCMR group also showing higher levels than the stable group(P<0.01).Both TCMR and ABMR groups had significantly higher blood urea nitrogen levels than the stable group(P<0.01),with no statistically significant difference between TCMR and ABMR groups(P>0.05).The estimated glomerular filtration rate(eGFR)was lower in both TCMR and ABMR groups compared with the stable group(both P<0.01).In routine blood tests,the ABMR group had lower hemoglobin,red blood cell count,and platelet count than the stable group(all P<0.05).The TCMR group had higher neutrophil percentage(P<0.05)and count(P<0.05)than the stable group,and the ABMR group had a higher neutrophil percentage than the stable group(P<0.05).The eosinophil percentage and count in the TCMR group were lower than in the stable and ABMR groups(all P<0.05).Both TCMR and ABMR groups had lower basophil percentage and count,as well as lower lymphocyte percentage and count,compared with the stable group(all P<0.05).There were no significant differences in monocyte percentage and count among the 3 groups(all P>0.05).In lymphocyte subpopulations,the TCMR and ABMR groups had lower counts of CD45+cells and T cells compared with the stable group(all P<0.05).The TCMR group also had lower counts of CD4+T cells,NK cells,and B cells than the stable group(all P<0.05).There were no significant differences in the T cell percentage,CD4+T cell percentage,CD8+T cell percentage and their counts,CD4+/CD8+T cell ratio,NK cell percentage,and B cell percentage among the stable,TCMR,and ABMR groups(all P>0.05). Conclusion:The occurrence of rejection leads to impaired transplant kidney function,accompanied by characteristic changes in some parameters of routine blood tests and peripheral blood lymphocyte subpopulations in kidney transplant recipients.The different characteristics of changes in some parameters of routine blood tests and peripheral blood lymphocyte subpopulations during TCMR and ABMR may help predict and diagnose rejection and differentiate between TCMR and ABMR.