Key result
The NSQIP method of measuring readmission from the date of surgery underestimated 30-day readmission rates by 9% to 36% compared to the CMS method of measuring from discharge.
Why the study?
The study was conducted to compare readmission rates measured by the Centers for Medicare and Medicaid Services with those measured by the American College of Surgeons National Surgical Quality Improvement Program.
Does the NSQIP method of measuring readmission underestimate rates compared to the CMS method in Medicare patients undergoing major surgery?
Cohort (n=299,249)
Does the NSQIP method of measuring readmission underestimate rates compared to the CMS method in Medicare patients undergoing major surgery?
Measuring 30-day readmissions from the date of surgery (NSQIP method) rather than discharge (CMS method) introduces an immortal-time bias that significantly underestimates readmission rates, particularly for procedures with longer lengths of stay.
Answers are grounded in this paper and cite their sources.
NSQIP and CMS 30-day readmission rates may not be interchangeable; leaves open a standardized start date for surgical quality metrics.
OBJECTIVE: To compare readmission rates as measured by the Centers for Medicare and Medicaid Services and the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) methods. DATA SOURCES: 20 percent sample of national Medicare data for patients undergoing cystectomy, colectomy, abdominal aortic aneurysm (AAA) repair, and total knee arthroplasty (TKA) between 2010 and 2014. STUDY DESIGN: Retrospective cohort study comparing 30-day readmission rates. DATA COLLECTION/EXTRACTION METHODS: Patients undergoing cystectomy, colectomy, abdominal aortic aneurysm repair, and total knee arthroplasty between 2010 and 2014 were identified. PRINCIPAL FINDINGS: Cystectomy had the highest and total knee arthroplasty had the lowest readmission rate. The NSQIP measure reported significantly lower rates for all procedures compared to the CMS measure, which reflects an immortal-time bias. CONCLUSIONS: We found significantly different readmission rates across all surgical procedures when comparing CMS and NSQIP measures. Longer length of stay exacerbated these differences. Uniform outcome measures are needed to eliminate ambiguity and synergize research and policy efforts.
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Hugar et al. (2019) conducted a cohort in Major surgery (cystectomy, colectomy, AAA repair, TKA) (n=299,249). NSQIP readmission measurement method (from index surgery) vs. CMS readmission measurement method (from index discharge) was evaluated on 30-day readmission rate (Relative difference of 9% to 36% lower readmission rates with NSQIP vs CMS, p=<.001). The NSQIP method of measuring readmission from the date of surgery underestimated 30-day readmission rates by 9% to 36% compared to the CMS method of measuring from discharge.
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