Initial Laboratory Workup for Ileus
For a patient presenting with suspected ileus, obtain a complete blood count, comprehensive metabolic panel (including electrolytes, renal function, liver function, and albumin), arterial or venous blood gas with lactate level, and coagulation profile. 1
Core Laboratory Panel
Hematologic and Metabolic Assessment
- Complete blood count (CBC) to detect leukocytosis (suggesting ischemia or perforation), anemia (indicating chronic disease or bleeding), and hemoconcentration (reflecting dehydration) 1
- Comprehensive metabolic panel including sodium, potassium, chloride, bicarbonate, blood urea nitrogen, creatinine, glucose, calcium, and magnesium to identify electrolyte derangements that directly impair intestinal motility and to assess for pre-renal acute kidney injury from volume depletion 1, 2
- Liver function tests (AST, ALT, alkaline phosphatase, bilirubin) and serum albumin to evaluate hepatic function and nutritional status 1
Markers of Ischemia and Perforation
- Arterial or venous blood gas with pH and lactate level as critical indicators of bowel ischemia—elevated lactate, metabolic acidosis (low bicarbonate and pH), and base deficit suggest tissue hypoperfusion and potential strangulation requiring urgent surgical intervention 1
- Serum amylase/lipase may be elevated in intestinal ischemia, though this is nonspecific 1
Coagulation Studies
- Prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR) should be obtained given the potential need for emergency surgery 1
Critical Interpretation Points
Electrolyte Abnormalities
The most clinically significant electrolyte derangements in ileus are hypokalemia, hyponatremia, and hypomagnesemia, as these directly suppress intestinal smooth muscle contractility and must be aggressively corrected to restore motility 2. Marked leukocytosis (>15,000-20,000/μL) combined with left shift suggests bowel ischemia or perforation rather than simple functional ileus 1.
Ischemia Indicators
The combination of elevated lactate (>2-4 mmol/L), metabolic acidosis (pH <7.35, bicarbonate <20 mEq/L), marked leukocytosis, and hyperamylasemia strongly suggests intestinal ischemia and mandates urgent surgical consultation 1. However, normal lactate does not exclude early ischemia, particularly in sigmoid volvulus where clinical deterioration can be rapid 1.
Hydration Status Assessment
Elevated blood urea nitrogen-to-creatinine ratio (>20:1), hemoconcentration (elevated hematocrit), and hypernatremia indicate significant volume depletion requiring aggressive crystalloid resuscitation 1, 2.
Additional Considerations Based on Clinical Context
Stool Studies (When Diarrhea Present)
If the patient has any diarrheal component or recent antibiotic exposure, obtain stool culture for bacterial pathogens, Clostridioides difficile testing (glutamate dehydrogenase antigen and toxin A/B), and stool for ova and parasites if travel history or endemic exposure exists 1, 3. Fecal calprotectin can help differentiate inflammatory bowel disease from functional disorders if the diagnosis is uncertain 1, 3.
Inflammatory Markers
C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) may be obtained to assess systemic inflammation, though these are nonspecific and do not reliably distinguish mechanical from functional ileus 1, 3.
Common Pitfalls to Avoid
Do not delay surgical consultation while waiting for laboratory results if the patient exhibits peritoneal signs, hemodynamic instability, or clinical deterioration 1, 2. Normal lactate and white blood cell count do not exclude bowel ischemia in its early stages, particularly within the first 6-12 hours 1. Hypokalemia and hypomagnesemia are frequently overlooked but critically impair intestinal motility and must be corrected concurrently with fluid resuscitation 2. The absence of fever or leukocytosis does not rule out ischemia, as elderly or immunocompromised patients may not mount typical inflammatory responses 1.