BMI and access to kidney transplantation in New Zealand: A retrospective cohort study

Background: Obesity prevalence is not only increasing worldwide but also in the dialysis population. Transplantation is the best form of kidney replacement therapy with improved patient survival, even for obese patients. A review of the literature found that internationally, access to transplantation may be limited for those with obesity. There is no research on obesity and access to transplantation in the New Zealand setting, particularly in Māori and Pacific people, who have higher rates of obesity and represent the largest prevalence of patients on dialysis. Aim: The following study aims to determine the association between body mass index (BMI) and access to kidney transplantation in New Zealand and to investigate whether there are any ethnic disparities. Methods: A retrospective cohort study utilised a de-identified data set from the New Zealand Blood Service (NZBS) and the Australia New Zealand dialysis and transplant registry (ANZDATA). Patients who commenced kidney replacement therapy (KRT) during the 10-years of 2010 – 2019, aged 16 to 65, were eligible for inclusion in the study. Results: Of the 3518 patients included in the study, 52% were obese. Multivariate analysis showed, that compared to a BMI < 25kg/m², a BMI 30 - 34.9 kg/m2 (obese category 1) was associated with a 34% increased likelihood of access to transplantation [aHR 1.34 (95% CI 1.15-1.57)]. A BMI 35 - 39.9 kg/m² was not associated with access to transplantation, however: a BMI ≥ 40 kg/m² was associated with a significantly lower chance of access to transplant [aHR 0.26 (95% CI 0.19-0.36)], in comparison to a BMI < 25kg/m². There was no association between BMI and time to transplant after waitlisting. Māori ethnicity was significantly associated with a decreased likelihood of access to transplantation and transplantation once listed, but there was no significant interaction between ethnicity, BMI, and access to transplantation. Conclusion: The association between BMI and access to transplantation in New Zealand varies between BMI categories, with a significant decrease in access at a BMI ≥ 40kg /m². A discussion needs to occur regarding policy review to determine whether there should be a BMI threshold for access to transplant or whether an individualised approach would be more appropriate. Further research needs to occur to identify the barriers for Māori in terms of access to transplantation and transplantation once listed to address the inequity of transplantation for tangata whenua.