This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn.

The use of laparoscopic gastric bypass (LGB) in the treatment of obese patients was examined. The surgical technique involved the use of a 21-mm circular stapler to create the gastrojejunostomy.

Treatment.

Cost-effectiveness analysis.

The study population comprised obese patients undergoing LGB.

The setting was a hospital. The economic study was carried out in the USA.

The effectiveness and resource use data were gathered from July 2002 to April 2003. The price year was 2003.

The effectiveness evidence was derived from a single study.

The costing was carried out on the same sample of patients as that included in the effectiveness study. It was carried out retrospectively in the pre-surgery phase and prospectively in the post-surgery phase.

Power calculations, if performed, were not reported. A sample of 50 consecutive patients was enrolled. There were 7 men and 43 women. The mean body mass index preoperatively was 51 (+/- 7) kg/m2 (range: 39 - 67). The mean patient age was 44.0 (+/- 9.4) years (range: 23 - 63). It was not stated whether some patients refused to participate or were excluded for any reason from the study sample.

This was a within-group comparison study that was carried out at a single institution, the Department of Surgery at the University of Wisconsin. The patients were followed for at least 6 months. Data referring to the 6-month pre-surgery period were also gathered retrospectively. No patient was lost to the follow-up assessment. No blinding was performed.

All of the patients included in the initial study sample were accounted for in the analysis of effectiveness. The primary outcome measure was the prevalence of selected co-morbid medical conditions before and after surgery. Co-morbid conditions included diabetes, hypertension, hypercholesterolaemia, GERD and depression. The excess weight loss after 6 months was also reported.

The mean excess weight loss after 6 months was 52% (+/- 11) (range: 35 - 82).

The prevalence of co-morbid medical conditions was:

for diabetes, 26% before and 4% after surgery, (p<0.01);

for hypertension, 46% before and 10% after surgery, (p<0.01);

for hypercholesterolaemia, 26% before and 0% after surgery, (p<0.01);

for GERD, 32% before and 4% after surgery, (p<0.01); and

for depression, 54% before and 54% after surgery, (p not significant).

The effectiveness analysis showed that LGB led to a significant reduction in the main co-morbidities for obese patients. The prevalence of depression did not change after surgery.

No summary benefit measure was used in the economic evaluation. In effect, a cost-consequences analysis was carried out.

The perspective adopted in the study was not stated. The economic evaluation included only prescribed medications. In particular, preoperative prescription medication consumption was compared with prescription medication consumption at the time of the routine 6-month post-surgery clinic visit. The costs of over-the-counter, non-prescription nutritional supplements such as multivitamins, calcium and vitamin B12, were excluded. The costs of diabetic supplies and blood glucose monitoring, as well as those associated with the treatment of sleep apnoea, were also not included. The cost of LGB was not taken into consideration. The protocol for post-gastric bypass medication adjustments was reported. The quantities of resources used were reported, whereas the unit costs were not. The unit costs were derived from an online pharmacy in October 2003, which was considered to be the price year. Resource consumption was derived from the sample of patients included in the effectiveness analysis. Discounting was not relevant since the costs were incurred during less than two years.

A statistical analysis of the medication costs was performed using the Wilcoxon rank sum test.

The indirect costs were not taken into consideration.

US dollars ($).

Sensitivity analyses were not performed.

See the 'Effectiveness Results' section.

The average number of medications per patient preoperatively was 3.7 (+/- 2.5). After surgery, patients took an average of 1.7 (+/- 1.6) prescription medications, (p<0.05).

The medication expenses associated with co-morbid conditions were:

for diabetes, $64.9 (+/- 88) before and $2.0 (+/- 7.1) after surgery (monthly cost-savings $62.9; p<0.05);

for hypertension, $45.0 (+/- 26.7) before and $8.4 (+/- 19.8) after surgery (monthly cost-savings $36.6; p<0.05);

for hypercholesterolaemia, $85.8 (+/- 34.5) before and $0 after surgery (monthly cost-savings $85.8; p<0.05);

for GERD, $110.6 (+/- 86.0) before and $19.2 (+/- 41.7) after surgery (monthly cost-savings $91.4; p<0.05); and

for depression, $107.1 (+/- 85.2) before and $107.1 (+/- 85.2) after surgery (monthly cost-savings $0; p not significant).

The cost of all prescription medications was $217.6 (+/- 189) before and $97.3 (+/- 107) after surgery (monthly cost-savings $120.3; p<0.05).

A synthesis of the costs and benefits was not relevant since a cost-consequences analysis was performed.

Laparoscopic gastric bypass (LGB) resulted in a significant improvement in co-morbid health conditions 6 months after surgery. It also led to substantial overall mean monthly cost-savings in prescription medication, especially in those with gastroesophageal reflux disease (GERD), hypertension, diabetes and hypercholesterolaemia. It was noted that the overall improvement in health and quality of life after LGB had been well documented in earlier studies, although the authors stated that the cost-effectiveness of gastric bypass surgery was difficult to demonstrate.

LGB was compared with no intervention, which consisted of medical management of obesity. You should decide whether this is a valid comparator in your own setting.

The effectiveness data came from a within-group comparison study, which was appropriate since no external comparison group was required. However, since the clinical outcomes were estimated in two different periods, factors other than the study intervention might have affected the clinical end points. The authors do not appear to have considered the potential impact of historical trends, although the period during which the effectiveness data were gathered was not overly long. The size of the sample was not justified by means of statistical tests. The patients were identified at a single institution, which might have limited how representative the study sample was. Thus, caution is required when extrapolating the results of the analysis to other patient populations. However, the inclusion of consecutive patients increases the robustness of the study. The use of a longer follow-up period would have been helpful. The analysis focused on the impact of the interventions on co-morbidities, which were therefore used as a proxy for patient health since no specific health-related measures were used as clinical end points. These issues tend to limit the internal validity of the analysis.

No summary benefit measure was used in the analysis because a cost-consequences analysis was conducted. Please refer to the comments in the 'Validity of estimate of measure of effectiveness' field (above).

The analysis of the costs was restricted to the cost-savings associated with the reduction in medication use for co-morbid conditions. Other costs, including the cost of surgery, were not considered. The perspective adopted in the study was unclear. The source of the costs was reported, but the unit costs were not given. Resource use was assessed from the sample of patients included in the trial. The costing was carried out retrospectively for the pre-surgery period. The price year was reported, which will facilitate reflation exercises in other settings.

The authors did not make extensive comparisons of their findings with those from other studies. They also did not address the issue of the generalisability of the study results to other settings. Sensitivity analyses were not performed, which limits the external validity of the analysis.

The study results support the use of LGB for the treatment of obese patients. The authors stated that more extended and comprehensive prospective comparative studies should be carried out to help prove that the expenses associated with bariatric surgery are justified.

None stated.

Craig BM, Tseng DS. Cost-effectiveness of gastric bypass for severe obesity. Am J Med 2002;113:491-8.

Fang J. The cost-effectiveness of bariatric surgery. Am J Gastroenterol 2003;98:2097-8.

Nguyen NT, Goldman C, Rosenquist J, et al. Laparoscopic vs. open gastric bypass: a randomized study of outcomes, quality of life, and costs. Ann Surg 2001;234:279-91.