What lab workup is recommended for patients with chronic constipation?

From the Guidelines

Lab workup for patients with chronic constipation should be limited to a complete blood cell count (CBC) in the absence of other symptoms and signs. This recommendation is based on the American Gastroenterological Association's medical position statement on constipation, which suggests that only a CBC is necessary in the absence of other symptoms and signs 1. The statement also recommends against metabolic tests, such as glucose, calcium, and sensitive thyroid-stimulating hormone, unless other clinical features warrant otherwise 1.

Key points to consider when evaluating patients with chronic constipation include:

• A colonoscopy should not be performed in patients without alarm features, such as blood in stools, anemia, or weight loss, unless age-appropriate colon cancer screening has not been performed 1
• Colonic transit should be evaluated if anorectal test results do not show a defecatory disorder or if symptoms persist despite treatment of a defecatory disorder 1
• The rationale for limited testing is that most chronic constipation is functional in nature, and extensive laboratory evaluation rarely changes management in patients without warning signs

In general, the approach to laboratory workup for chronic constipation should be guided by the patient's clinical presentation, with more comprehensive evaluation reserved for those with concerning features or who fail to respond to initial management strategies.

From the Research

Lab Workup for Chronic Constipation

The lab workup for chronic constipation typically involves a combination of tests to evaluate the underlying causes of the condition. The following are some of the key tests that may be recommended:

• Colonic transit time with radiopaque markers to assess the movement of food through the colon 2
• Anorectal manometry with balloon expulsion test to evaluate the function of the anal sphincter and pelvic floor muscles 2, 3, 4
• Digital rectal examination to assess the tone and sensation of the anal sphincter and rectum 4
• Bristol stool scale to evaluate the consistency and shape of the stool 4
• Colonic scintigraphy to assess the movement of food through the colon 4
• Wireless motility capsule for assessment of colonic and whole gut transit 4
• High resolution anorectal manometry to evaluate the function of the anal sphincter and pelvic floor muscles 4
• Colonic manometry to assess the function of the colon 4

Indications for Testing

Testing is typically recommended for patients who do not respond to initial treatments, such as dietary fiber and laxatives 3, 5. The choice of test depends on the patient's symptoms and medical history. For example:

• If a defecatory disorder is suspected, testing with balloon expulsion or anal manometry may be considered 3
• If colonic dysmotility is suspected, colonic transit time and colonic manometry may be recommended 5
• If pelvic floor dysfunction is suspected, anorectal manometry and biofeedback therapy may be recommended 2, 5

Interpretation of Test Results

The results of these tests can help guide the diagnosis and treatment of chronic constipation. For example:

• A delayed colonic transit time may indicate slow-transit constipation 2
• Abnormal anorectal manometry results may indicate pelvic floor dysfunction 2, 3
• Normal test results may indicate functional constipation or irritable bowel syndrome with constipation 2