Validation of the SF-36 as a measure of postoperative recovery after colorectal surgery

Surgery is evolving, and new techniques are introduced to improve "recovery." Postoperative recovery is complex, and evaluating the effectiveness of surgical innovations requires assessment of patient-reported outcomes. The Short-Form-36 (SF-36), a generic health-related quality of life questionnaire, is the most commonly used instrument in this context. The objective of this study was to contribute evidence for the validity of the SF-36 as a metric of postoperative recovery. Data from 128 patients undergoing planned colorectal surgery at one university hospital between 2005 and 2010 were analyzed. In the absence of a gold standard, the responsiveness and construct validity (known groups and convergent) of the SF-36 were evaluated. Standardized response means were computed for the former and non-parametric tests were used to assess the statistical significance of the changes observed. Multiple linear regression was used to determine whether the SF-36 discriminates between patients with versus without complications and between laparoscopic and open surgery (known groups); correlations between the SF-36 and the 6-min walk test, a measure of functional walking capacity (convergent) was investigated with Spearman's rank correlation. The SF-36 was sensitive to clinically important changes. Scores on six of eight domains and the physical component summary score deteriorated postoperatively (SRM 0.86 for the PCS, p < 0.01) and improved to baseline thereafter. Patients with complications had significantly lower scores on five SF-36 domains (with differences from -9 (-18, -1), p = 0.04 to -18 (-32, -2), p = 0.03), and scores on all subscales were lower than those in a healthy population (p < 0.01 to p = 0.04). The SF-36 did not differentiate between laparoscopic and open surgery. Physical functioning scores correlated with 6MWT distance at 1 and 2 months (Spearman's r = 0.31 and 0.36, p < 0.01). The SF-36 is responsive to expected physiological changes in the postoperative period, demonstrates construct validity, and thus constitutes a valid measure of postoperative recovery after planned colorectal surgery. The SF-36 did not, however, discriminate between recovery after laparoscopic and open surgery.