To our knowledge, the present study is the first population-based retrospective cohort study that estimated the five-year direct medical costs and comorbidities after bariatric surgery in Hong Kong. Above all, findings of this study provided additional information on direct medical costs in an Asian context, and provided basis for further cost-effectiveness analysis of bariatric surgery among obese Chinese patients with type 2 diabetes. Indeed, most existing costing analyses on bariatric surgery were conducted in the US [20–22], and those results may be inappropriate to be generalized to other jurisdictions, where mandatory insurance cover is not available and/or population ethnicities are totally different. Therefore, information on annual direct medical costs, healthcare utilization and medication use of bariatric patients provided by this study was especially important for policy makers and bariatric surgeons in Asian countries to further optimize the health resources allocation. Besides, comorbidity profiles of both groups were tracked for 60 months, providing an overview of changes of comorbidities. Also, as most previous comparative cost analyses on bariatric surgery did not include exploratory analyses [20, 22, 36, 37], this study also added current knowledge on medical costs of bariatric patients in subgroups, which allowed easy estimation of annual direct medical costs of surgical patients with different health conditions.
One major finding of the present study was that surgical patients had significantly higher medical costs in the year of surgery but had lower annual costs in the subsequent four years. This was mainly because surgical patients had great expenditures on bariatric procedures and bariatric surgery-related hospitalization, while control patients did not have such cost considerations. However, in the remaining years, shorter length of hospital stays were found in the surgery group in year 2 onwards. Indeed, coefficients in Supplemental Table 6 indicated that bariatric surgery was associated with increased medical costs in year 1 (p < 0.001). However, the values of coefficients were below zero in the following years, suggesting that bariatric surgery was associated with reduced medical costs. Despite the surgical patients having need to use outpatient and allied health professional services more frequently than non-surgical patients over the years, the unit cost of hospitalization was much higher than that of outpatient visits and allied health professional visits. Consequently, the costs saved from outpatient and allied health services by the matched control group were considerably less than the extra costs of hospitalization, leading to the higher medical spending for the control group in the subsequent years. However, the finding that bariatric surgery was associated with reduced costs of inpatient services was inconsistent with the results of previous comparative studies [21, 22, 37], where higher hospitalization costs were reported in post-surgery periods. One possible explanation to this discrepancy is that re-operation rates of in patients with bariatric surgery was relatively low in Hong Kong. Indeed, the overall re-operation rate in the present surgical group was 4.74% in the index year and nearly zero in year 3 onwards (Supplemental Table 7). In comparison, reported re-operation rates in a systematic review is around 7% . Besides, decreased frequencies of prescription and saved diabetes medication in the bariatric surgery group were observed in the first 4 years after bariatric surgery. Similar findings were also reported in previous studies, which suggested that the mean number of diabetes medication per patient and number of patients with prescriptions dropped after bariatric surgery over time [20, 39, 40].
Though bariatric surgery had cost-saving effects in year 2 onwards, the five-year cumulative medical costs of surgical patients were higher than those of matched control patients, as saved costs failed to offset the increased costs due to bariatric surgery. However, the slope of the curve representing the cumulative costs of controls was steeper than that of surgical patients (Fig. 2), indicating that a possible break-even point may occur during the post-surgery period. Cumulative costs of surgical patients and controls were expected to converge at year 22 after the index date. In other words, cumulative medical costs of non-surgical patients would catch up those of surgical patients at year 22 if other conditions remain unchanged. However, as the baseline age of included patients in this study was around 53, the cohorts would turn to 75 at the break-even year. Geriatric diseases that need intensive care may happen in their 70’s and could incur more annual medical costs.
Of note, the relative differences of five-year cumulative costs between surgical and non-surgical patients were smaller in subgroups of patients who were female, had baseline age over 60 years old, had BMI over 35 kg/m2, had diagnosis of type 2 diabetes over 5 years, had CCI greater than 4, had history of CVD, and had history of CRD. These results implied shorter time to break-even may occur in these subgroups, and therefore obese type 2 diabetes patients in these subgroups were more suggested to undergo bariatric surgery. Notably, patients with CRD in the surgery group had similar 5-year cumulative medical costs with those in the control group. One possible explanation was that bariatric surgery has renal protective effects, even in patients with established renal diseases [38, 41, 42]. Improved renal function after bariatric surgery largely reduced the annual medical costs of surgical patients in post-surgery years, and facilitated cumulative costs of CRD patients with and without bariatric surgery approximately converge at year 5. Another possible reason was that treating CRD patients, especially those with end-stage renal disease, is costly . Therefore, costs of bariatric operation for those patients accounted for 11.6% of the 5-year total medical costs when compared to 36.3% of total costs in overall.
Our study also supported that bariatric surgery delayed the occurrence of most comorbidities and improved profiles of comorbidity, since fewer percentage of surgical patients proceed towards high CCI categories and surgical patients had lower mean CCI across 5 years. Particularly, bariatric surgery had protective effects on hypertension, hyperlipidemia, musculoskeletal and chronic orthopedic disorders, CVD, severe hypoglycemia, chronic lung disease and CRD. Indeed, previous studies have already reported that bariatric surgery was beneficial towards resolving or delaying above comorbidities [9, 38, 42].
Several potential limitations in the present study should be acknowledged. Firstly, we included patients who had used HA healthcare services from 2006 to 2017. However, patients whose index year was 2014 or later have not yet completed their five-year follow-up. Consequently, the smaller sample size affected the estimation of annual medical costs in later years, and some findings should be interpreted with caution. Secondly, unlike a few previous studies , the present one did not differentiate the type of bariatric surgical procedures, but presented results in overall. Lastly, this study was based on the data obtained from HA, which is the public health service provider in Hong Kong. Hence, the annual direct medical costs of obese patients with type 2 diabetes attending private health services were not included.