Comparison of subjective classification of stool consistency and stool water content*1

Objective: The purpose of this study was to compare the stool consistency categorizations made by 39 adults with fecal incontinence and the percentage of water in their stools determined by lyophilization. Methods: Subjects collected all stools daily for 8 days during a baseline period and at the end of a fiber treatment period. Stool consistency was recorded as hard and formed, soft but formed, loose and unformed, or liquid, Aliquots of the stools were lyophilized to constant weight. Main Outcome Measures: The main outcome measures were the percentage of stool water among stools in each consistency category and the correlation between subjects' stool consistency categorizations and the percentage of stool water. Results: The subjects were 8 men and 21 women, ranging in age from 30 to 89 years, who were participating in a study of the effectiveness of dietary fiber for treating fecal incontinence. A total of 1023 stool samples were analyzed. Significant differences in the mean percentage of water were found among the 4 stool consistency categories (hard and formed = 68% ± 0.9%, soft but formed = 74% ± 0.3%, loose and unformed = 80% ± 0.4%, and liquid = 85% ± 0.3%; P < .001). Ninety-six percent of the stools had a percentage of water within 2 SDs of the mean percentage of water of other stools in their consistency category. Conclusion: This classification system of stool consistency is a valid and practical measure for clinical studies. It may be useful for clinicians and patients to evaluate outcomes of treatments directed at improving stool consistency.