Measuring substantial reductions in functioning in patients with chronic fatigue syndrome.

Purpose: All the major current case definitions for chronic fatigue syndrome (CFS) specify substantial reductions in previous levels of occupational, educational, social, or personal activities to meet criteria. Difficulties have been encountered in operationalizing 'substantial reductions.' For example, the Medical Outcomes Study Short Form-36 Health Survey (SF-36) has been used to determine whether individuals met the CFS disability criterion. However, previous methods of using the SF-36 have been prone to including people without substantial reductions in key areas of physical functioning when diagnosing CFS. This study sought to empirically identify the most appropriate SF-36 subscales for measuring substantial reductions in patients with CFS.

Method: The SF-36 was administered to two samples of patients with CFS: one recruited from tertiary care and the other a community-based sample; as well as a non-fatigued control group. Receiver operating characteristics were used to determine the optimal cutoff scores for identifying patients with CFS.

Results: The SF-36 Role-Emotional subscale had the worst sensitivity and specificity, whereas the Vitality, Role-Physical, and Social Functioning subscales had the best sensitivity and specificity.

Conclusion: Based on the evidence from this study, the potential criteria for defining substantial reductions in functioning and diagnosing CFS is provided.