Six studies were included in the review: three case series, two case-control studies, and one retrospective study of abdominal radiographs. The total number of participants could not be determined from the data presented.
The total scores for methodological quality ranged from 5 to 11 (mean 8.3) out of 14. The least fulfilled criteria related to disease progression bias (one study fulfilled this criterion) clinical review bias (two studies fulfilled this criterion) and the reporting of intermediate test results (no studies fulfilled this criterion). Inter-observer reliability, for the rating of plain radiographs, was evaluated in three studies, and ranged from moderate (k=0.52) to excellent (k=0.85). All six studies were conducted in hospital settings.
One study presented a logistic regression model, where clinical symptoms of constipation were the independent variables and radiographic constipation the dependent variable. The model defined a clinical diagnosis of constipation. This diagnosis was present 1.2 times as often in children with radiographic constipation as in those without (positive LR 1.2, 95% CI: 1.0, 1.4).
Four studies assessed the ability of abdominal radiography to distinguish between children with and without clinical constipation. Only one study reported a statistically significant discriminatory value, a positive LR of 3.0 (95% CI: 1.6, 4.3). One further study reported only accuracy as a measure of discriminatory value (accuracy 80%, 95% CI: 50, 100). The authors reported that 'low quality' studies generally reported higher diagnostic value than 'high quality' studies (observation derived from visual examination of the results plotted in ROC space).
Two studies presented data on the diagnostic value of individual symptoms in relation to faecal impaction on abdominal radiography. One low-quality study found a significant positive LR for a history of hard stools (LR 1.2, 95% CI: 1.0, 1.4). The other high-quality study found a significant positive LR for rebound tenderness (LR 1.1, 95% CI: 1.0, 1.2). The two studies reported conflicting data on the value of rectal examination; the high-quality study found a statistically significant association (LR 1.6, 95% CI: 1.2, 2.0) and the low-quality study found no significant association (LR 1.5, 95% CI: 0.8, 2.3).