Mana H. Vriesman, Carlos A. Velasco-Benitez, Carmen R. Ramirez, Marc A. Benninga, Carlo Di Lorenzo, Miguel Saps

To assess the agreement between the Questionnaire on Pediatric Gastrointestinal Symptoms-Rome III (QPGS-RIII) and the Bristol Stool Scale (BSS) in evaluating stool consistency and the diagnosis of functional constipation in children. Children aged 8-18 years were asked to describe their stool consistency in the previous month according to the QPGS-RIII and the BSS. Stool consistency according to both instruments was categorized into 3 categories: "hard," "normal," and "liquid." The children's reported stool consistency using the QPGS-RIII and the BSS were compared, and the intrarater agreement between the 2 instruments was measured using the Cohen kappa coefficient (κ). The diagnosis of functional constipation was based on the Rome III criteria, incorporating the assessment of stool consistency according to the QPGS-RIII and the BSS. A total of 1835 children were included. Only slight agreement existed between the QPGS-RIII and the BSS for assessing stool consistency (κ = .046; P = .022). Significantly more children reported hard stools on the BSS compared to the QPGS-RIII (18.0% vs 7.1%; P = .000). The prevalence of functional constipation was 8.6% using the QPGS-RIII and 9.3% using the BSS (P = .134). Only slight agreement exists between the QPGS-RIII and the BSS in the evaluation of stool consistency in children. Better instruments are needed to assess the consistency of stools with a high degree of reliability, both in research and in the clinical setting.