Abstract BACKGROUND AND AIMS Metabolic syndrome (MetS) is a condition that promotes arteriosclerosis due to various arteriosclerosis risk factors such as impaired glucose tolerance, impaired lipid metabolism and hypertension, caused by insulin resistance as a result of visceral fat obesity. There have been several epidemiological studies on MetS after renal transplantation conducted in the U.S. and Europe, indicating that MetS is an accumulation of non-immunological risks of renal transplantation, which affects the patient's prognosis as well as that of the kidney. However, the incidence of MetS in Japanese renal transplant recipients is 20 to 30% and lower compared with that of American and European recipients, and its effects on cardiovascular complications and kidney prognosis are not clear. We report on the results of our long-term longitudinal study on MetS in renal transplant recipients. METHOD A total of 104 renal transplant outpatients, over 6 months after their transplants and in stable condition, were diagnosed with MetS from January 2006 and June 2007 and followed up until December 2020. The effects of MetS on outcomes including renal and cardiovascular events were studied using four diagnostic criteria [NCEP-ATP III (Japanese, original, Asian) and IDF criteria]. We performed multivariate Cox proportional hazards regression analysis to examine the association between the presence or absence of MetS and combined vascular events in renal transplant recipients. This study protocol was conducted in accordance with the Principles of the Declaration of Helsinki and the Declaration of Istanbul, and was approved by the ethics committee of Osaka City University (No. 2020–197). All analyses were performed using R ver. 4.0.3 (https://www.r-project.org/foundation/) with the ‘rms’ and ‘RcmdrPlugin.EZR’ packages. RESULTS The incidence of MetS among our renal transplant recipients in our baseline investigation was 24.0% by the NCEP-ATP III (Japanese) criteria, and our longitudinal study showed that MetS was a significant risk factor even after adjustment of background factors using the propensity score (HR: 2.82; 95% CI: 1.26–6.34, P = 0.012). In addition, the effects of MetS diagnosed using the NCEP (original), NCEP (Asian) and IDF criteria on cardiac composite events were HR: 2.39; 95% CI: 1.07–5.38, P = 0.035, HR: 2.35; 95% CI: 1.00–5.55, P = 0.051, and HR: 1.90; 95% CI: 0.84–4.31, P = 0.12, respectively. CONCLUSION Although the incidence of MetS in Japanese renal transplant recipients was lower compared to that of American and European renal transplant recipients, our results indicated that MetS also affected cardiovascular complications and kidney prognosis in Japanese renal transplant recipients. Moreover, depending on the diagnostic criteria for MetS, the HR was shown to be around 2.0–3.0.
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