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Surg Obes Relat Dis. 2014 Sep-Oct;10(5):774-9. doi: 10.1016/j.soard.2014.04.006. Epub 2014 Apr 18.

Predicting 90-day mortality after bariatric surgery: an independent, external validation of the OS-MRS prognostic risk score.

Author information

Group Health Research Institute, Seattle, Washington. Electronic address:
Kaiser Permanente Center for Health Research, Portland, Oregon.
Kaiser Permanente Georgia Center for Health Research Southeast, Atlanta, Georgia.
The Permanente Medical Group, Kaiser Permanente Northern California, San Francisco, California.
Kaiser Permanente Colorado Institute for Health Research, Denver, Colorado; University of Colorado School of Medicine, Aurora, Colorado.



The Obesity Surgery Mortality Risk Score (OS-MRS) was developed using data from 1995 to 2004; it has yet to be validated for more recent patients in integrated delivery system settings. The objective of this study was to validate the OS-MRS using data from electronic health records in a distributed data network.


We conducted a retrospective cohort study of 3,817 adults who underwent an open (21.4%) or laparoscopic (78.6%) gastric bypass surgery between 2005 and 2007 in the Scalable Partnering Network. Our main outcome was all-cause mortality during the 90 days after surgery. We scored patients' risk of mortality by adding characteristics according to the OS-MRS (i.e., 1 point for each predictor).


Sixteen of 3,817 (0.42/100; 95% CI, .24-.68) patients died within 90 days. The OS-MRS discriminated low-risk and high-risk patients effectively: low-risk (2 of 1,654 patients; .12 deaths/100 patients), intermediate-risk (10 of 2,008 patients; .50 deaths/100 patients), and high-risk (4 of 155 patients; 2.58 deaths/100 patients). High-risk patients were 21.3 times more likely to die in the first 90 days after surgery than low-risk patients (risk ratio = 21.3; 95% CI, 3.9-115.6).


In these 10 U.S. healthcare delivery systems, the OS-MRS appears valid-albeit with the caveat that we observed a small number of deaths. The OS-MRS appears useful for identifying the small fraction of patients at high risk for 90-day mortality after open and laparoscopic RYGB.


Bariatric surgery; Gastric bypass; Mortality; Obesity; Prognostic risk score

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