Tests
1st tests to order
complete blood count (CBC)
Test
Indicated when there are clinical suspicions of secondary causes of constipation.
Result
usually normal; decreased hemoglobin, microcytosis indicating anemia, especially iron deficiency anemia, suggests a secondary cause
thyroid function tests
Test
Indicated when there are clinical suspicions of secondary causes of constipation.
Result
usually normal; increased or decreased thyroid-stimulating hormone (TSH) suggests a secondary cause
serum electrolytes, calcium, and magnesium
Test
Indicated when there are clinical suspicions of secondary causes of constipation.
Result
usually normal; hypercalcemia, hypokalemia, hypomagnesemia, or other electrolyte problems suggest a secondary cause
blood glucose
Test
Indicated when there are clinical suspicions of secondary causes of constipation.
Result
usually normal; elevated blood glucose suggests a secondary cause
quantitative fecal immunochemical test
Test
UK guidelines recommend quantitative fecal immunochemical testing (FIT) to guide referral for suspected colorectal cancer in adults with a change in bowel habit.[43] If FIT result is ≥10 micrograms hemoglobin/g feces, refer patients urgently. Referral should not be delayed if there is a strong clinical suspicion (e.g., due to abdominal mass) and FIT is negative or if patients do not return their sample.[43]
Result
usually normal; positive results suggests a secondary cause
abdominal x-ray
Test
Optional during initial evaluation.
Indicated when there are clinical suspicions of secondary causes of constipation.
Can be helpful in assessing colonic stool load in obese patients where physical exam is difficult.
Result
fecal impaction, rectal masses
barium enema
Test
Optional during initial evaluation.
Indicated when there are clinical suspicions of secondary causes of constipation.
Result
fecal impaction, rectal masses
Tests to consider
barium defecography
Test
Evaluates anorectal angle at rest and during straining, perineal descent, anal diameter, indentation of the puborectalis, amount of rectal and rectocele emptying.[18][45]
As this procedure involves exposure to high levels of radiation, the clinician should exercise caution in obtaining this test, especially in women with child-bearing potential.
The distinction between normal and abnormal pathology is challenging at times because normative data are scarce.[18]
Barium and MR defecography should be considered complementary.[18] In one Cochrane review of imaging studies in women with symptoms of obstructed defecation, the pooled sensitivity for barium defecography compared to MR defecography for evaluating pelvic floor descent was 98% versus 94%, and pooled specificity was 83% versus 79%, respectively.[49]
Result
incomplete evacuation of the rectum, poor rectal stripping wave, abnormal perineal descent
magnetic resonance defecography
Test
Simultaneously evaluates global pelvic floor anatomy and dynamic motion, to evaluate for rectocele, enterocele, rectal prolapse, and other pelvic floor dysfunctions.[46][47][48]
The distinction between normal and abnormal pathology is challenging at times because normative data are scarce.[18]
Barium and MR defecography should be considered complementary.[18] In one Cochrane review of imaging studies in women with symptoms of obstructed defecation, the pooled sensitivity for barium defecography compared to MR defecography for evaluating pelvic floor descent was 98% versus 94%, and pooled specificity was 83% versus 79%, respectively.[49]
Result
incomplete evacuation of the rectum, poor rectal stripping wave, abnormal perineal descent
colonoscopy
Test
Indicated only in the presence of rectal bleeding, heme-positive stool, iron deficiency anemia, weight loss, obstructive symptoms, recent onset of symptoms, rectal prolapse, or change in stool caliber, and in patients age >50 years who have not previously had colon cancer screening.[42]
Result
intraluminal masses, strictures, or luminal obstruction
colonic transit study
Test
Physiologic testing is indicated if the clinical evaluation does not determine a cause and/or there is a lack of response to initial medical therapy, so that further therapy can be tailored toward the underlying pathophysiology.
Result
retention of >20% of radio-opaque markers on an abdominal x-ray performed 120 hours after ingestion of the capsule indicates slow colonic transit; retention of a wireless motility capsule for >59 hours after capsule ingestion also provides an accurate assessment of colonic transit time
anorectal manometry
Test
Physiologic testing is indicated if the clinical evaluation does not determine a cause and/or there is a lack of response to initial medical therapy, so that further therapy can be tailored toward the underlying pathophysiology.
Result
dyssynergia, impaired/absent recto-anal inhibitory reflex, abnormal rectal sensation (hypo- or hypersensitivity)
balloon expulsion studies
Test
Physiologic testing is indicated if the clinical evaluation does not determine a cause and/or there is a lack of response to initial medical therapy, so that further therapy can be tailored toward the underlying pathophysiology.
Result
inability to expel a 50 mL saline-filled balloon within 60 seconds indicates a probable diagnosis of dyssynergia
colonic manometry
Test
Indicated as part of the preoperative evaluation for colectomy for severe refractory constipation.
Result
neuropathy: absence of high-amplitude propagated contractions plus absent waking or gastro-colonic responses; myopathy: attenuated or disordered responses
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