Fluid intake and urinary osmolality in pediatric patients with functional constipation.

PURPOSE This study aimed to evaluate fluid intake and urinary osmolality in pediatric patients with functional constipation. METHODS This was a cross-sectional, case-control study that prospectively included two groups: 36 pediatric patients older than 4 years with functional constipation (Rome III criteria) who were consecutively admitted in a public tertiary pediatric gastroenterology outpatient clinic and 93 controls with normal bowel habits. The control group was recruited from a public school and did not have any of the characteristics of the Rome III criteria. Fluid and food intakes were assessed using a daily diet inquiry and 24 h recording method. Hypohydration was defined as osmolality greater than 800 mOsm/kg H2O in a spot urine sample. RESULTS The age of the functional constipation group (median, 8.9 years; range 7.3-10.0 years) and the control group (8.8 years) was similar (p = 0.51). The proportion of boys in the functional constipation group (76.6%; 25/36) was higher (p = 0.01) than that in the control group (45.2%; 41/93). The total water intake of the functional constipation group (median 1566 mL) was lower (p < 0.001) than that of the control group (median 2177 mL). Urinary osmolality was higher (p = 0.039) in the functional constipation group (median 859 mOsm/kg H2O) than in the control group (median 775 mOsm/kg H2O). The association between hypohydration and functional constipation did not reach statistical significance (Odds ratio 2.06; 95% confidence interval 0.93-4.55; p = 0.073). CONCLUSION Compared to the control group, patients with functional constipation have lower fluid intake and higher urinary osmolality.