Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Diabetes Center, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Diabetes Obes Metab. 2024 Oct;26(10):4273-4280. doi: 10.1111/dom.15771. Epub 2024 Jul 16.
Non-randomized studies on bariatric surgery have reported large reductions in mortality within 6-12 months after surgery compared with non-surgical patients. It is unclear whether these findings are the result of bias.
We searched PubMed to identify all non-randomized studies investigating the effect of bariatric surgery on all-cause mortality compared with non-surgical patients. We assessed these studies for potential confounding and time-related biases. We conducted bias analyses to quantify the effect of these biases.
We identified 21 cohort studies that met our inclusion criteria. Among those, 11 were affected by immortal time bias resulting from the misclassification or exclusion of relevant follow-up time. Five studies were subject to potential confounding bias because of a lack of adjustment for body mass index (BMI). All studies used an inadequate comparator group that lacked indications for bariatric surgery. Bias analyses to correct for potential confounding from BMI shifted the effect estimates towards the null [reported hazard ratio (HR): 0.78 vs. bias-adjusted HR: 0.92]. Bias analyses to correct for the presence of immortal time also shifted the effect estimates towards the null (adjustment for 2-year wait time: reported HR: 0.57 vs. bias-adjusted HR: 0.81).
Several important sources of bias were identified in non-randomized studies of the effectiveness of bariatric surgery versus non-surgical comparators on mortality. Future studies should ensure that confounding by BMI is accounted for, considering the choice of the comparator group, and that the design or analysis avoids immortal time bias from the misclassification or exclusion.
与非手术患者相比，减重手术的非随机研究报告称，手术后 6-12 个月内死亡率大幅降低。目前尚不清楚这些发现是否存在偏倚。
我们在 PubMed 上搜索了所有非随机研究，以确定比较减重手术与非手术患者对全因死亡率影响的研究。我们评估了这些研究是否存在潜在的混杂和与时间相关的偏倚。我们进行了偏倚分析，以量化这些偏倚的影响。
我们确定了 21 项符合纳入标准的队列研究。其中，11 项受到不朽时间偏倚的影响，这是由于对相关随访时间的错误分类或排除。由于缺乏对体重指数（BMI）的调整，有 5 项研究存在潜在的混杂偏倚。所有研究均使用了缺乏减重手术指征的不适当的对照组。为校正 BMI 引起的潜在混杂而进行的偏倚分析使效应估计值向零值靠拢[报告的风险比（HR）：0.78 与偏倚校正 HR：0.92]。校正不朽时间存在的偏倚分析也使效应估计值向零值靠拢（调整 2 年等待时间：报告的 HR：0.57 与偏倚校正 HR：0.81）。
在非随机研究中，与非手术对照组相比，减重手术在死亡率方面的有效性存在几个重要的偏倚来源。未来的研究应确保校正 BMI 混杂，考虑到对照组的选择，并在设计或分析中避免因错误分类或排除而导致的不朽时间偏倚。
