Constipation: Diagnosis

Careful history and rectal examination can establish the diagnosis, and physical examination may help identify causes of secondary constipation.

Identification of drug side effects in adults, including over–the–counter products such as antacids and iron supplements, does not negate the need for further evaluation—for example, in patients at risk for colorectal cancer. Drugs may make evident a problem that had not previously been apparent.

A detailed bowel diary, submitted by a patient or parent, may be helpful. Many people misjudge normal bowel function as abnormal.

Laboratory evaluation is indicated if hypothyroid disease, anorexia, hypercalcemia, or diabetes is suspected. These conditions may also apply in children, as may celiac disease, lead poisoning, cystic fibrosis, and urinary tract infection.

Plain film imaging of the abdomen can detect megacolon/rectum and assist in monitoring progress in a hospitalized patient. However, in cases of intra–abdominal bowel distention, plain films often cannot distinguish ileus from mechanical obstruction.

If history and physical examination are normal, colonoscopy or barium enema can help rule out obstruction. Gastrografin should be used if perforation or partial obstruction is suspected. Barium can become desiccated behind a partial obstruction. 

Final diagnostic steps may include:

Marker studies to determine normality of colon transit 

Anorectal manometry to assess the appropriateness of internal and external anal sphincter tone, and intrarectal pressure during defecation.