Fluid intake and urinary osmolality in pediatric patients with functional constipation

This study aimed to evaluate fluid intake and urinary osmolality in pediatric patients with functional constipation.

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.

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).

Compared to the control group, patients with functional constipation have lower fluid intake and higher urinary osmolality.