The Constipation Severity Instrument: A Validated Measure

Abstract

This study was designed to develop and test the validity and reliability of the Constipation Severity Instrument. Scale development was conducted in two stages: 1) 74 items were generated through a literature review and focus groups of constipated patients and medical providers; and 2) a preliminary instrument was administered to 191 constipated patients and 103 healthy volunteers. Test-retest reliability of the constipated group was assessed (N=90). Content, convergent, divergent, and discriminant validity were evaluated by using other validated measures by performing one-way analysis of variance and Pearson correlations. Exploratory and confirmatory factor analysis revealed three subscales: obstructive defecation, colonic inertia, and pain. Internal consistency (alpha=0.88-0.91) and test-retest reliability (intraclass correlation coefficients=0.84-0.91) were high for all subscales. Constipated patients were grouped by Rome II criteria: functional constipation (22 percent), pelvic floor dyssynergia (15 percent), constipation predominant irritable bowel syndrome (23 percent), and no specific criteria (40 percent). Those with constipation predominant irritable bowel syndrome or pelvic floor dyssynergia scored higher on the Obstructive Defecation and Colonic Inertia subscales than those with functional constipation or no specific criteria (P=0.001-0.058). Subjects with functional constipation had much lower scores on the pain subscale than constipation predominant irritable bowel syndrome, functional constipation, or no specific criteria (P<0.009). The Constipation Severity Instrument subscale and total score correlated very highly with the subscales and total score of the Patient Assessment of Constipation Symptom measure. The Constipation Severity Instrument subscales discriminated well between constipated patients and healthy volunteers (P<0.001) and demonstrated excellent divergent validity. Higher Constipation Severity Instrument scores inversely correlated with general quality of life. The Constipation Severity Instrument is a reliable and valid instrument for assessing constipated patients. Administration of the Constipation Severity Instrument to other constipated patients will further validate its use.