Tests
1st tests to order
abdominal CT scan
Test
CT scan of the abdomen is the initial imaging investigation in patients with suspected intestinal obstruction.[17] The sensitivity of abdominal CT scan in detecting intestinal obstruction is 84% to 95%, depending on the degree of obstruction.[20] CT scan has a high (approximately 90%) accuracy in predicting intestinal strangulation and therefore the need for urgent surgery.[21]
CT is useful in diagnosing complications of SBO, including ischemia, strangulation or necrosis.[16][20][21][22] It can also detect underlying malignancy as a cause of SBO.[9]
A multidetector CT scanner and multiplanar reconstruction can be used, if available. They aid in the diagnosis and localisation of the SBO.[1][23]
Result
may visualize transition zone, mass, tumor, appendicitis
CBC
Test
May indicate potential severe intestinal obstruction with necrosis.
A low hematocrit may indicate blood loss caused by an underlying disease.
Result
increased WBC, rarely decreased hematocrit
BUN
Test
An increase in the urea shows the severity of dehydration/renal failure in complicated SBO.
Result
increased in the setting of volume depletion
electrolyte panel
Test
Electrolyte imbalance is consistent with dehydration.
Result
may show hyponatremia, hypokalemia, metabolic alkalosis, and metabolic acidosis
Tests to consider
abdominal x-rays
Test
Abdominal x-rays may be considered in the initial evaluation of patients with suspected intestinal obstruction, particularly in patients who are hemodynamically unstable or unable to undergo cross-sectional imaging, or who have equivocal clinical findings. Studies testing the sensitivity of abdominal x-rays for detecting SBO have shown widely divergent results.[19] In addition, they likely will not give information about the etiology of obstruction, and findings may be normal in patients with early or proximal obstruction.[17] As such, they could prolong the evaluation period.[19] Upright and supine x-rays of the abdomen help to determine whether the patient has a partial or complete SBO, and whether obstruction is simple or complicated:[1]
Partial SBO: gas throughout the abdomen and into the rectum.
Complete SBO: no distal gas, and staggered air-fluid levels.
Complicated SBO: free air under the diaphragm suggestive of perforation; thumb-printing of the bowel suggestive of ischemia.
Result
may be normal; may show air-fluid levels, dilated intestinal loops, absence of gas in the rectum (in complete SBO), pneumoperitoneum
water-soluble contrast study
Test
In patients with acute SBO as a result of adhesions, water-soluble contrast challenge may help estimate whether conservative treatment has been successful. Patients in which the contrast reaches the colon by 24 hours rarely require surgery.[19][24][25]
Involves the administration of water-soluble contrast material into the stomach. The subsequent assessment of the degree of passage of this material, using serial x-rays, can provide information regarding the presence and location of the obstruction within the gastrointestinal tract:
In partial SBO, the medium passes into rectum.
In complete SBO, the medium does not pass into rectum and is held up at the site of obstruction.
Also demonstrates the extent of disease in patients with Crohn disease.
Result
presence or absence of contrast in the colon on abdominal x-ray
laparotomy/laparoscopy
Test
May be performed for patients in whom it is difficult to distinguish between simple and complicated SBO, or between SBO and some other cause of abdominal pain.
Result
appendicitis, malrotation, tumor mass
abdominal ultrasound
Test
This test is rarely performed in adult patients with SBO unless the diagnosis of underlying abdominal mass or appendicitis is suspected, and CT scanning is not available or cannot be performed. The dilated loops of bowel filled with gas and fluid invariably obscure any useful detail that may be obtained by ultrasound. However, it is a useful diagnostic modality in children.
Result
may show a mass, or inflamed/perforated appendix
abdominal MRI
Test
This test is rarely performed in patients with acute SBO. Can be useful in chronic, recurrent, or subacute cases, such as in Crohn disease or in pregnant women, to aid diagnosis while avoiding ionizing radiation.
Result
may show transition zone at point of obstruction, mass
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