Things We Do for No Reason™: Obtaining an Abdominal X-ray to Assess for Constipation in Children

Many systematic reviews and retrospective studies have investigated the efficacy of abdominal x-rays for diagnosing constipation. One retrospective review involving 160 children with defecation complaints assessed the accuracy of different radiologic scoring methods in identifying children with constipation.⁶ Three pediatric gastroenterologists and 1 pediatric radiologist blindly applied 4 scoring methods: colonic transit time, Leech score, Barr score, and fecal loading. The results showed that all x-ray scoring methods had low sensitivity for diagnosing constipation, variable specificity, and low interobserver reproducibility of scores.⁶ There was also poor ability to differentiate between patients with constipation and nonretentive fecal incontinence. Fecal loading had the worst performance in differentiating between these 2. Greater than 20% of children with clinically diagnosed constipation had normal Barr and Leech scores.⁶ Another systematic review also found no evidence for a diagnostic association between clinical symptoms of constipation and fecal loading on abdominal x-rays.⁷ In this study, the sensitivity and specificity of the x-ray were as low as 61% and 55%, respectively, which indicate poor overall diagnostic accuracy. Abdominal x-rays are subjective, not standardized, and represent a single observation in time. The amount of fecal loading seen on imaging is subject to daily variation depending on the timing of last food intake and timing of last defecation. There is a large variance in interpretation of fecal loading, and any stool seen on an x-ray does not rule out another potential diagnosis causing abdominal pain.

In 2014, the North American Society for Pediatric Gastroenterology, Hepatology, & Nutrition (NASPGHAN) and the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) released joint clinical guidelines that the evidence supports not obtaining an abdominal x-ray to diagnose functional constipation.⁸ Similarly, the National Institute for Health and Care Excellence (NICE) stated that abdominal x-rays should not be recommended as an additional test for constipation in children.⁹ These groups advocate for diagnosing functional constipation clinically by using a careful history and physical exam.

The primary patient harm associated with abdominal x-rays is radiation exposure. While the amount of radiation in a single x-ray is low, children with constipation tend to have frequent revisits, significantly more than children with other common chronic conditions (eg, asthma and migraine headaches).¹⁰In accordance with an “As Low As Reasonably Achievable” (ALARA) concept for radiation dose, all imaging should be limited to studies that will contribute to patient care.⁴ The low sensitivity and specificity of abdominal x-rays in identifying constipation challenges whether any new information is being obtained from the imaging. Frequent visits and repeated unnecessary radiographs mean increased exposure to radiation and higher healthcare costs. Moreover, abdominal x-rays in the pediatric emergency room have been associated with missed diagnoses, false reassurance of constipation, more frequent admissions into the hospital, and longer hospital stays.

One multicenter retrospective cohort study that included approximately 282,000 children diagnosed with constipation found that children who received an abdominal x-ray were twice as likely to return to the emergency department with a clinically significant alternate diagnosis (0.33% vs 0.17%). The 2 most common missed diagnoses were acute appendicitis and intussusception.³ Another retrospective study that included about 3,700 children also found that x-rays were performed more frequently in children who were misdiagnosed than in those who did not have a significant alternate diagnosis (75% vs 46%).¹¹ In this case, both of these groups had a similar amount of stool on the x-rays as determined by the mean Leech scores. While this study identified an association between abdominal x-ray use and misdiagnoses, a causative effect was not necessarily discovered between the 2. The authors felt that even relatively large amounts of stool on an x-ray should not discount serious causes of abdominal pain or tenderness.¹¹ A third retrospective study determined that children who received an abdominal x-ray and were diagnosed with constipation were significantly more likely to be admitted to the hospital, further raising healthcare costs.¹² In this study, having an x-ray reduced the odds of being discharged home by about half. They also found that abdominal x-rays could be avoided if digital rectal exams were performed.¹²