A total of 29 studies were included in the review. No studies addressed the utility of biochemical or haematological tests, or plain abdominal X-ray. One study (563 patients) assessed colonoscopy and two (96 patients and 26 controls) assessed barium enema. The remaining studies assessed one or more methods of physiologic testing: 10 studies (805 patients and 21 controls) assessed colonic transit testing, 9 studies (665 patients and 61 controls) assessed anorectal manometry, 9 studies (608 patients and 67 controls) assessed the balloon expulsion test, and 10 studies (760 patients and 56 controls) assessed defecography.
No study assessed the routine use of blood tests or abdominal X-ray. No study reported the use of a reference standard to confirm diagnosis.
Flexible sigmoidoscopy or colonoscopy (1 study; quality score of 3). One retrospective study of colonoscopy for cancer surveillance found colonic cancer in 1.4% of patients and polyps in 14.6%.
Barium enema (2 studies; quality scores of 3 and 4).
In one study no patients with constipation were diagnosed with organic disease, while in the other, constipation was just as likely to be present in patients with a normal test as in those where the test was abnormal (odds ratio 0.94, 95% confidence interval: 0.61, 1.44).
Studies of physiological testing showed differences in population, methodology and interpretation. Few studies assessed tests blindly and few were prospective series of consecutive patients.
Colonic transit time (10 studies, quality scores of 3 to 5): studies of colonic transit testing showed a prevalence of 38 to 80% for slow transit constipation.
Anorectal manometry (9 studies; quality scores of 4 or 5): studies of anorectal manometry showed a prevalence of 20 to 75% dyssynergia.
Balloon expulsion test (9 studies; quality scores of 3 to 5): studies of balloon expulsion testing showed impaired expulsion in 23 to 67% of patients.
Defecography (10 studies; quality scores of 3 to 5): studies of defecography reported abnormalities in 25 to 90% of patients and dyssynergia in 13 to 37%.