The Relative Influence of Surgical Disease and Co-Morbidities on Patient Responses to a Generic Health-Related Quality-of-Life Instrument EMILY FRANCE, B.S., VIC VELANOVICH, M.D. From the Division of General Surgery, Henry Ford Hospital, Detroit, Michigan Generic health-related quality-of-life (QoL) instruments are increasingly used to assess the out- comes of surgical interventions. However, it is unclear to what extent the patient’s associated comorbidities have on the responsiveness of these instruments to measure changes caused by the operation. The purpose of this study was to assess the relative influence of comorbidities to surgical disease in how patients answered the items of the most frequently used generic instru- ment, the SF-36. Sixty-nine preoperative patients completed the SF-36, which contains 36 items covering eight domains and a health transition question. For each of the 36 items, patients were asked to rate the influence of their surgical disease and their comorbidities on how they answered the items from 1 to 10. The surgical disease, comorbidities, and medications were recorded. Data was analyzed using the Mann-Whitney U test and linear regression analysis. Of the 36 items of the SF-36, patients reported that their surgical disease influences nine items greater than their comorbidities (P \ 0.05). Using linear regression analysis, the number of comorbidities did not effect the influence of the surgical disease in any item; however, this number had a direct rela- tionship (P \ 0.05) with the influence of comorbidities on how the patient answered the item. However, the magnitude of the influence was low. There was an inverse (negative slope, P \ 0.05) relationship between the number of comorbidities and the score of six of eight domains. Although the surgical disease has more of an influence on how patients answered the items of the SF-36, as the number of comorbidities increased, these seem to have more influence. Therefore, the SF-36 would be a good choice for assessing QoL in most surgical disease. However, as the overall magnitude of this influence was low, this may be a cause of the lack of responsiveness of generic QoL instruments in measuring the effect of operations on QoL. Importantly, as the number of comorbidities increased, the scores of the SF-36 decreased, implying that the effect of the surgical disease would be greater in patients with fewer comorbidities. H EALTH-RELATED QUALITY -OF-LIFE (QoL) is an ever increasingly used endpoint in assessing surgical outcomes. QoL is generally measured using ques- tionnaires. Patients answer each question (referred to as an item) and their qualitative responses are con- verted to a numerical scale for quantitative analysis. 1 There are three types of QoL instruments: generic (meant to be applicable across patient populations and disease processes), disease-specific (meant to be applicable to the effects of a single disease), and symptom severity (meant to measure the intensity of symptoms without its effects on other aspects of QoL). 2 Each has its advantages and disadvantages. In surgical research, generic instruments are com- monly used. The most popular of these is the SF-36, a generic QoL instrument measuring eight domains of QoL with a ‘‘health transition’’ item. These eight domains can then be grouped into a physical compo- nent and a mental health component. 3 A PUBMED search of the literature using the phrase SF-36 and surgery identified over 1600 articles. Therefore, it is clear that QoL instruments, in general, and the SF-36, in particular, are important components in the assess- ment of surgical outcomes. There are many factors involved in the effective use QoL instruments in surgical research. One of the most important is that of responsiveness, sometimes called sensitivity to change. 4 This is the ability of the instrument to detect changes in QoL over time or due to an intervention. In surgery, the intervention of interest is usually an operation. However, it is not always the case that generic instruments are sensitive Address correspondence and reprint requests to Vic Velanovich, M.D., Division of General Surgery K-8, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202. E-mail: vvelano1@ hfhs.org. 1084