AbstractBackgroundBariatric surgery can be effective in weight reduction and diabetes remission in some patients, but is expensive. The costs of bariatric surgery in patients with obesity and type 2 diabetes mellitus (T2DM) were explored here.MethodsPopulation-based retrospectively gathered data on patients with obesity and T2DM from the Hong Kong Hospital Authority (2006–2017) were evaluated. Direct medical costs from baseline up to 60 months were calculated based on the frequency of healthcare service utilization and dispensing of diabetes medication. Charlson Co-morbidity Index (CCI) scores and co-morbidity rates were measured to compare changes in co-morbidities between surgically treated and control groups over 5 years. One-to-five propensity score matching was applied.ResultsOverall, 401 eligible surgical patients were matched with 1894 non-surgical patients. Direct medical costs were much higher for surgical than non-surgical patients in the index year (€36 752 and €5788 respectively; P < 0·001) mainly owing to the bariatric procedure. The 5-year cumulative costs incurred by surgical patients were also higher (€54 135 versus €28 603; P < 0·001). Although patients who had bariatric surgery had more visits to outpatient and allied health professionals than those who did not across the 5-year period, surgical patients had shorter length of stay in hospitals than non-surgical patients in year 2-5. Surgical patients had significantly better CCI scores than controls after the baseline measurement (mean 3·82 versus 4·38 at 5 years; P = 0·016). Costs of glucose-lowering medications were similar between two groups, except that surgical patients had significantly lower costs of glucose-lowering medications in year 2 (€973 versus €1395; P = 0.012).ConclusionBariatric surgery in obese patients with T2DM is expensive, but leads to an improved co-morbidity profile, and reduced length of hospitalization.