Investigations
1st investigations to order
computed tomography
Test
Order a CT scan of the abdomen and pelvis with oral and intravenous contrast according to local hospital protocols.[4][11][14][16]
Use the CT scan to identify the level and cause of the obstruction, and therefore determine the management plan.[4]
CT scans have a high (approximately 90%) accuracy in predicting intestinal strangulation and therefore the need for urgent surgery.[14] CT is also useful in diagnosing ischaemia.[26]
The detail that a CT provides with regard to the severity and aetiology of the obstruction will help to establish the management plan.[11]
Use a multidetector CT scanner and multiplanar reconstruction, if available.They aid in the diagnosis and localisation of small bowel obstruction.[11][31]
Result
may visualise transition zone, mass, tumour, appendicitis; CT evidence of a non-adhesional cause (tumour, hernia, volvulus, or gallstone) or evidence of bowel ischaemia is an indication for surgery;[4] conservative treatment may be indicated if the CT fails to demonstrate a mechanical cause for the symptoms[4]
water-soluble contrast study
arterial blood gases (including lactate)
Test
Perform an arterial blood gas and take a lactate reading.[4]
Result
an elevated lactate reading indicates poor tissue perfusion; it is not diagnostic for intestinal ischaemia
full blood count
Test
Perform an FBC to understand and manage the metabolic consequences of small bowel obstruction.
Result
WBC count >10,000/mm3 is a non-specific marker of inflammation;[14] a low haematocrit may indicate blood loss through an underlying disease or into obstructed bowel, a potential sign of intestinal necrosis
electrolytes
Test
An elevated urea and creatinine may indicate dehydration.
Measure and document hydration status in all patients presenting with symptoms of acute bowel obstruction in order to minimise the risk of acute kidney injury.[16]
Electrolyte imbalances are often seen in patients with bowel obstruction – in particular, low potassium.[4][14]
Patients on renal dialysis can have symptoms of ileus due to electrolyte imbalance.[32]
Result
hyponatraemia, hypokalaemia, metabolic alkalosis
C-reactive protein
urea/creatinine ratio
Test
Dehydration may result in acute kidney injury.[14]
Result
elevated levels suggest dehydration/hypovolaemia and increased risk for development of severe disease
serum lipase or amylase
Test
Use serum lipase testing (if available) in preference to serum amylase.[33][34]
Serum lipase and amylase have similar sensitivity and specificity but lipase levels remain elevated for longer (up to 14 days after symptom onset versus 5 days for amylase), providing a higher likelihood of picking up a diagnosis of pancreatitis in patients with a delayed presentation.[35]
Acute pancreatitis is an important differential diagnosis for a patient presenting with acute, severe abdominal pain.
Result
a result >3 times the upper limit of the normal range confirms the diagnosis of acute pancreatitis in a patient with acute upper abdominal pain[36]
glucose
clotting, group and save, or cross-match
Test
Required if surgery is anticipated.[4]
Result
consider your hospital guidelines or consult with haematology
Investigations to consider
urine or serum beta–human chorionic gonadotrophin (HCG)
Test
Perform in women of childbearing age.
Result
consult with gynaecology if positive[4]
urinalysis
Test
Perform if urinary symptoms are present.
Do not diagnose a urinary tract infection by urinalysis alone.
Check for ketones in urine if you suspect diabetic ketoacidosis (DKA).[37][38]
DKA can present with abdominal pain.[37] DKA consists of the biochemical triad of ketonaemia (ketosis), hyperglycaemia, and acidaemia.
Result
ketonaemia >3.0 mmol/L or significant ketonuria (2+ or more on standard urine sticks) indicates DKA[38]
ECG
Test
Perform an ECG on patients over 50 years of age, or those with a history of cardiac disorder.[4]
Result
may show arrhythmias
magnetic resonance imaging
Test
May be useful in place of CT in pregnant women, where CT is contraindicated.
Result
may show transition zone at point of obstruction, or a mass
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