Tests
1st tests to order
CT abdomen and pelvis
Test
Diagnosis of obstruction can be confirmed in >90%.[35] CT is the preferred confirmatory diagnostic study for both cecal and sigmoid volvulus and should be ordered as soon as possible when a diagnosis of large bowel obstruction is suspected.[3][8][13]
CT with multiplanar reconstruction can diagnose volvulus with near 100% sensitivity and 90% specificity.[13]
Diagnosis of obstruction is confirmed by colonic dilation. Colonic segments differ in normal diameter, but established limits are: 10 to 12 cm for cecum (beyond which the risk of perforation increases); 8 cm for ascending colon; and 6.5 cm for rectosigmoid.
May also reveal underlying cause and provide more diagnostic information than contrast enema.[8][29]
Demonstrates pathology extrinsic to the large bowel and is particularly useful in colorectal carcinoma, where it assesses disease stage. In case of a perforation diagnosis on abdominal x-ray in a stable patient, an abdominal CT scan could be considered in order to define the cause and site of perforation. A CT scan, however, should not delay appropriate treatment. Early involvement of the surgeon is required to help make the decision to proceed with CT.[5] Do not use a protocol that involves contrast-enhanced CT acquisition in addition to unenhanced acquisition except in certain circumstances (such as gastrointestinal hemorrhage), as unenhanced images do not add diagnostic information.[30]
Result
may visualize obstruction, perforation, dilatation, ischemia, malignancy; evidence of a nonadhesional cause (tumor, hernia, or volvulus). In acute diverticulitis, CT scan may show localized inflammation, abscess formation, perforation, obstruction of fistulation into the bladder or vagina. Excludes pseudo-obstruction.
CBC
Test
Elevated WBC count may indicate an infective or inflammatory cause or complication, such as perforation or impending perforation.
Anemia may be found in the presence of an underlying malignancy and is of a microcytic/iron-deficiency picture. Present in 30% to 75% cases of colorectal cancer.[18][42][43][44]
Result
elevated WBC count, possible anemia
serum electrolytes
Test
May be deranged from dehydration, fluid shifts, or sepsis.
Derangement depends on duration and onset of obstruction.
Colon secretes potassium and bicarbonate in exchange for sodium chloride and water absorption, and this is disrupted in the obstructed colon, which may produce hypokalemia.
Result
variable
CRP
Test
Check for elevated CRP.
Result
elevated CRP (>75 mg/L) may indicate inflammation.
renal function
Test
BUN is elevated above normal limits to a greater degree than creatinine, depending on premorbid renal function.
Result
elevated BUN or creatinine
glucose
Test
It is important to check blood glucose level because diabetic ketoacidosis (DKA) can present with abdominal pain.[31] DKA consists of the biochemical triad of ketonemia (ketosis), hyperglycemia, and acidemia.
See our topic Diabetic ketoacidosis.
Result
blood glucose 250 mg/dL, as one of the triad of biochemical signs, indicates DKA.
coagulation studies, type and screen, cross-match
Test
Coagulopathy may be present in sepsis from perforation. Request type and screen and consider cross-match if surgery is anticipated.
Result
prolonged INR, PTT, and prothrombin time
arterial blood gas (including lactate)
Test
An arterial blood gas should be requested in all critically sick patients, to obtain a lactate reading.
Result
an elevated lactate reading indicates poor tissue perfusion. It is not diagnostic for intestinal ischemia. Lactic acidosis may indicate perforation or necrosis.
serum amylase/lipase
Test
Can be elevated with any significant intra-abdominal event.
Result
elevated
plain abdominal x-ray
Test
Abdominal plain x-ray is a screening test in bowel obstruction and is often used initially for diagnosis.[3][5] An x-ray may show the colon distended to the point of the obstruction with a paucity of distal gas or signs more classically associated with colonic volvulus. Colonic segments differ in normal diameter, but established limits are: 10-12 cm for cecum (beyond which the risk of perforation increases); 8 cm for ascending colon; and 6.5 cm for rectosigmoid.
[Figure caption and citation for the preceding image starts]: Large bowel obstruction. Plain radiograph showing distended large bowel loops. Note grossly dilated caecum (white arrow)Musson RE, Bickle I, Vijay RKP, et al. Gas patterns on plain abdominal radiographs: a pictorial review. Postgrad Med J. 2011 Apr;87(1026):274-87; used with permission [Citation ends].
Level of obstruction may be determined by a cut-off beyond which the colon or rectum is empty of gas.
Colonic volvulus is identified in approximately 75% of x-rays; characteristic kidney- or coffee bean shape seen with the "apex" locating the origin of volvulus (e.g., sigmoid, cecal).[33][34]
Sigmoid volvulus: dilated inverted U-shaped loop of colon (resembling a coffee bean or bent inner tube) projecting toward the right side of abdomen; opposing colonic walls produce radio-opaque line; proximal large and small bowel dilation may also be evident.[8]
Cecal volvulus: dilated right colon rotates to the left side and dilated small bowel may also be present.
[Figure caption and citation for the preceding image starts]: Abdominal radiograph showing dilated large bowel loops. Typical "coffee bean’"sign seen for sigmoid volvulusRoy SP, Tay YK, Kozman D. Very rare case of synchronous volvulus of the sigmoid colon and caecum causing large-bowel obstruction. BMJ Case Rep. 2019 Jan 28;12(1):bcr-2018-227375; used with permission [Citation ends].
Plain abdominal x-ray is not an accurate method for confirming a malignant etiology for the obstruction.
In patients with an incompetent ileocecal valve, an x-ray may also show a distended small bowel with air-fluid levels suggestive of small bowel obstruction.[3]
Foreign body ingestion may also be identified on plain abdominal x-ray. One of the limitations of abdominal plain x-ray is the risk of false negatives of pneumoperitoneum when a small amount of intraperitoneal free air is present (e.g., in the case of early perforation at the tumor site).[5]
Intramural gas ominously suggests colonic ischemia.
Result
gaseous distension of large bowel; dilated inverted U-shaped loop (resembling a coffee bean or bent inner tube) seen in volvulus
Tests to consider
beta-human chorionic gonadotrophin
Test
Urine or serum beta-human chorionic gonadotrophin (hCG) should be performed in in women of childbearing age.[32]
Result
consult with gynecology if positive to rule out ectopic pregnancy.
urinalysis
Test
Perform if urinary symptoms are present.[32] Urinary tract infection should not be diagnosed by urinalysis alone.
Check for ketones in urine if DKA is suspected.[31]
Diabetic ketoacidosis (DKA) can present with abdominal pain.[31] DKA consists of the biochemical triad of ketonemia (ketosis), hyperglycemia, and acidemia.
See our topic Diabetic ketoacidosis.
Result
ketonemia >3 mmol/L or significant ketonuria (more than 2+ on standard urine sticks) indicates DKA.
abdominal ultrasound
Test
Large bowel obstruction may also be diagnosed using ultrasound (performed by radiologists or as point of care), although the diagnostic criteria are not as well defined as for small bowel obstruction.[27][28]
One proposed criteria include dilated large intestine (> 4.5 cm) and presence of abdominal A-lines (gastrointestinal intraluminal air).[28] Point-of-care ultrasound (POCUS) also has the advantage that it can be performed by nonradiologists at the bedside as a noninvasive diagnostic tool without radiation but does require specialized training.
Result
may show dilated large intestine (>4.5cm) and abdominal A-lines (gastrointestinal intraluminal air).
contrast enema
Test
May be performed after initial assessment to confirm diagnosis, although a CT scan is typically the study of choice and is more readily available.
Provides information on the level, degree, and type of obstruction.[5]
Water-soluble contrast flows freely to obstruction, where there is a characteristic cut-off point depending on the nature of obstruction.
Contrast ends as a bird's beak in colonic volvulus, which confirms diagnosis (where doubt exists on abdominal x-ray).[3]
Contraindicated if perforation or peritonitis is suspected.
Result
obstruction to contrast at site of lesion; "bird's beak" appearance seen with volvulus
flexible/rigid endoscopy
Test
Main indication is when plain radiology strongly indicates volvulus. Confirms the diagnosis and is a therapeutic measure.[3][5][13] For patients with uncomplicated sigmoid volvulus, the American Society for Gastrointestinal Endoscopy and World Society or Emergency Surgery suggests endoscopy as the initial treatment modality.[8][13]
For obstructing malignant lesions in the left and rectosigmoid colon, flexible endoscopy can confirm the diagnosis based on endoscopic features and with biopsy, and may also have a therapeutic role if the lesion is amenable to stenting or dilation.[37][38][39]
Result
normal luminal mucosa or nonviable mucosa; in sigmoid volvulus, endoscopy may visualize the classic mucosal pinwheel at the point of obstruction before detorsion
biopsy
Test
Confirms malignancy. Is typically adenocarcinoma, although other subtypes exist.[45]
Sampling error may result in false-negatives so should be taken in context of clinical appearance.
Result
malignant histopathology
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