Background: Functional status is considered an important measure of health status in primary care. The COOP-WONCA charts, which comprise six single-item scales, have mainly been used to determine functional ability in chronically ill patients.
Aim: A study was carried out to determine whether the charts are able to measure the degree of functional impairment associated with acute illness and the improvement in functional ability accompanying the process of recovery.
Method: A total of 95 patients presenting with acute low back pain were recruited from 15 single-handed general practices in northern Germany. At presentation and at two-week follow up, these patients completed self-administered questionnaires which included the COOP-WONCA charts. The charts ask patients to use the timescale of the past two weeks when rating their condition. Baseline and follow-up measurements of the charts were compared and correlations of chart scores with patients' measurements of pain intensity on a visual analogue scale, general practitioners' ratings of impairment and patients' measurements of recovery were analysed.
Results: Only the chart measuring change in health revealed a deterioration in functional ability associated with the onset of pain and an improvement in functional status at follow up. Two of the other charts indicated a deterioration at follow up. Only the chart measuring change in health was correlated with ratings of pain and impairment at baseline. At follow up, strong correlations were found between general practitioners' assessments of impairment, patients' ratings of pain and patients' ratings of recovery for all scales except for those measuring social activities and daily activities. The patients interpreted the instructions for using the COOP-WONCA charts differently; some included the period of acute back pain while others did not.
Conclusion: Of the six charts only the change in health chart proved to be a suitable scale for measuring short-term changes in functional ability among general practice patients with acute low back pain. This may partly be a result of patients misunderstanding the instructions. If the COOP-WONCA charts are used with acutely ill patients, the fixed two-weeks timescale is not appropriate. It is suggested that patients consider their present complaints when rating their condition.