Hypothyroidism is not a frequent cause of constipation in children (JPGN 2012; 54: 285-87).  According to this study, the yield on checking for hypothyroidism in pediatric patients with constipation is no greater than in the general population.

This retrospective study examined the records of 873 patients who underwent thyroid testing ordered by pediatric gastroenterology; 443 (51%) had isolated constipation.  In all, 56 had abnormal thyroid function testing though 40 were normal on repeat testing. Of these 16 remaining cases, 7 were known to have hypothyroidism.  Of the nine remaining “new” cases, 3 had slow growth (2 without constipation), 3 had trisomy 21, and 2 were taking medications which affect thyroid function.  This leaves only 1 patient who presented with constipation without a clear risk factor or other indication for testing.

The authors state that 1/443 (0.2%) is quite similar to background incidence of hypothyroidism (0.3%).  The costs of identifying this case would exceed $18,000 but could be considered much higher (~$200,000) when all of the costs of false-positives are considered (eg. endocrinology consultations, followup testing).  In patients with slow growth (with or without constipation), about 2.5% had hypothyroidism.

In short, think twice about checking thyroid status in patients with isolated constipation.

Additional references:

• -JPGN 2011; 53: S2. 49, 55. ‘Rarely do children with constipation need w/u’–only if alarming features: Delayed meconium, bilious vomiting, bloody stools, fever, bladder disorders, poor growth, NO RESPONSE to conventional treatment, abnormal exam. 25% of functional constipation problems may persist into adulthood.
• -JPGN 2010; 51: 155. Lack of utility of AXR -suggested only in uncooperative pts, concerns about abuse/concerns about psychologic impact of exam
• -J Pediatr 2010; 156: 461-5. MRI in children with chronic constipation or not-retentive soiling (n=130, n=28) -MRI showed lumbar sacral abnormalities in 3% –none required neurosurgery (1 w spina bifida occulta, 3 w terminal filum lipomas). Prospective study.
• JPGN 2006; 43: e1Ye13.  http://www.naspghan.org/user-assets/Documents/pdf/PositionPapers/constipation.guideline.2006.pdf  Guidelines suggest checking thyroid, calcium, celiac and lead if not responding to therapy.