• Andrew L Rosenberg, Timothy P Hofer, Cathy Strachan, Charles M Watts, and Rodney A Hayward.
• University of Michigan and the Department of Veterans Affairs Health Services Research & Development Service, Veterans Affairs Ann Arbor Healthcare System, Ann Arbor, Michigan 48109-0048, USA. arosen@umich.edu
• Ann. Intern. Med. 2003 Jun 3;138(11):882-90.

BackgroundCommon methods of benchmarking clinical performance rarely, if ever, account for admission source and, in particular, the effect of a patient being transferred from one medical center to another. Small biases in comparisons of observed versus expected deaths can substantially affect how high-quality institutions compare with peer hospitals. With the most sophisticated and validated set of case-mix measures available for patients, the intensive care unit is an ideal setting in which to study the effect of a patient's being transferred from another hospital.ObjectiveTo determine the extent of bias in benchmarking outcomes when performance measures do not account for transfer patients' greater severity of illness.DesignProspectively developed cohort study.SettingMedical intensive care unit (MICU) at a tertiary care university hospital.Patients4579 consecutive admissions for 4208 patients from 1 January 1994 to 1 April 1998.MeasurementsMICU and hospital lengths of stay, MICU readmission, and hospital mortality rates.ResultsCompared with directly admitted patients, MICU patients transferred from another hospital had significantly higher Acute Physiology Scores at the time of admission and discharge (P = 0.001). Even after full adjustment for case mix and severity of illness, transfer patients had a 38% longer MICU stay (95% CI, 32% to 45%), a 41% longer hospital stay (CI, 34% to 50%), and a 2.2 times greater odds of hospital mortality (CI, 1.7 to 2.8) than directly admitted patients. With identical efficiency and quality, a referral hospital with a 25% MICU transfer rate compared with another with a 0% transfer rate would be penalized by 14 excess deaths per 1000 admissions when a benchmarking program adjusts only for case mix and severity of illness and not for the source of admission.ConclusionsIn a setting with the most thorough diagnostic-based, case-mix adjustment and the most physiologically precise severity-of-illness information, accepting transfer patients can adversely affect efficiency and quality benchmarks. Benchmarking and profiling efforts beyond intensive care units must also recognize and account for this phenomenon; otherwise, referral centers may have an incentive to refuse care for patients who could benefit from being transferred to their facility.

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