Regional variation in the risk of lower-limb amputation among patients with diabetes in New Zealand

Background: Lower-limb amputation is one of the most substantial and debilitating consequences of diabetes mellitus; however, the risk of lower-limb amputation is not equally shared across the diabetic population. The aims of this study were to (i) describe regional variation in the rate of lower-limb amputation in New Zealand among a national prevalent cohort of patients with diabetes; and (ii) explore the plausible factors that could be contributing to this variation.

Methods: Our cohort were the national prevalent cohort of individuals with diabetes in New Zealand in 2011, according to the Virtual Diabetes Register (n = 215 676). Using descriptive analysis and Poisson regression, we compared the rate of lower-limb amputation within each of New Zealand's 20 District Health Boards with the national rate of amputation, adjusting for demographic, health care access and patient-level factors.

Results: We observed nearly four-fold variation in the rate of major lower-limb amputation between regions in New Zealand, as well as nearly two-fold variation in the rate of minor lower-limb amputation. Adjustment for differences between regions in terms of ethnicity reduced this variation substantially for many District Health Boards. Despite adjustment for sex, age, ethnicity, deprivation, rurality, comorbidity and prior amputation, the rate of lower-limb amputation in a number of District Health Boards remained substantially higher than the national rate.

Conclusions: These observations could help to inform the funding and provision of diabetic foot care services across New Zealand; however, more work is required to further untangle the drivers of national variation in rates of lower-limb amputation.