Which baseline and ongoing investigations should be performed for a patient with acute pancreatitis in the intensive‑care unit?

Investigations for Acute Pancreatitis in the ICU

All patients with severe acute pancreatitis in the ICU require a structured baseline and ongoing investigation protocol that includes immediate laboratory markers, early ultrasound for etiology, and delayed contrast-enhanced CT at 72-96 hours to assess necrosis and guide intervention.

Baseline Investigations on Admission

Laboratory Tests

• Serum lipase is the first-line enzyme test, with a diagnostic cutoff >3 times the upper limit of normal providing the highest specificity for acute pancreatitis 1
• Liver function tests (bilirubin, AST, ALT, alkaline phosphatase) must be obtained to assess for biliary etiology 1, 2
• Serum triglycerides should be measured, as levels >1,000 mg/dL (11.3 mmol/L) indicate hypertriglyceridemia as the causative factor 1
• Serum calcium to evaluate for hypercalcemia-induced pancreatitis 1
• Hematocrit is critical, as values >44% represent an independent risk factor for pancreatic necrosis 1
• Blood urea nitrogen (BUN) >20 mg/dL serves as an independent predictor of mortality 1
• APACHE II score should be calculated, with a score >8 indicating severe disease and guiding ICU triage decisions 1, 2

Imaging Studies

• Transabdominal ultrasound should be performed on admission or within the first 48 hours to determine biliary etiology (gallstones, biliary obstruction) 3
• Chest and abdominal plain x-rays should be obtained routinely to exclude alternative diagnoses such as perforated viscus, intestinal obstruction, leaking abdominal aortic aneurysm, and mesenteric ischemia 4
• Chest x-ray specifically identifies complications including pleural effusion and acute respiratory distress syndrome (ARDS), which directly impact mortality and guide respiratory support decisions 4

Ongoing Investigations at 48-72 Hours

Severity Assessment Markers

• C-reactive protein (CRP) ≥150 mg/L measured at 48-72 hours after symptom onset is the preferred laboratory marker for predicting severe acute pancreatitis 3, 1
• A peak CRP >210 mg/L within the first 4 days achieves approximately 80% accuracy in predicting severe disease 1
• Serial CRP measurements combined with rising leukocyte counts and increasing APACHE II scores should prompt urgent reassessment for possible sepsis 1

Definitive Imaging for Severe Disease

• Contrast-enhanced CT (CE-CT) or MRI is mandatory for all patients with severe acute pancreatitis, with optimal timing at 72-96 hours after symptom onset 3, 1
• Early CT (<72 hours) underestimates pancreatic necrosis and should be avoided unless diagnostic uncertainty exists 3, 1
• CE-CT after 72 hours is the gold standard for assessing the extent of (peri)pancreatic necrosis, which is essential for determining prognosis and need for intervention 3

Investigations for Suspected Complications

Detection of Infected Necrosis

• Procalcitonin is the most sensitive laboratory test for detecting pancreatic infection, with low values being strong negative predictors of infected necrosis 1
• Image-guided fine needle aspiration (FNA) should be performed in patients with persistent symptoms and >30% pancreatic necrosis, or those with smaller areas of necrosis and clinical suspicion of sepsis 3
• FNA has an accuracy of 89-100% for establishing the diagnosis of infected necrosis 5

Additional Etiologic Workup for Unknown Causes

• Magnetic resonance cholangiopancreatography (MRCP) or endoscopic ultrasound should be considered to screen for occult common bile duct stones in patients with unknown etiology 3

Critical Timing Considerations

Do not delay escalation of care while awaiting investigation results if the patient exhibits clinical deterioration (organ failure, prolonged ileus, systemic signs); management decisions must be based on the clinical picture regardless of pending laboratory values 1. Persistent organ failure must be documented for over 48 hours to distinguish it from transient organ failure, which does not require ICU transfer 3.

Common Pitfalls to Avoid

• Do not rely on abdominal x-ray findings to diagnose acute pancreatitis, as they are unreliable and non-specific 4
• Do not perform CT before 72 hours unless there is diagnostic uncertainty, as it will underestimate necrosis and not modify early management 3
• Do not use CRP values obtained before 48 hours, as they underestimate severity 1
• Approximately 50% of patients will be misclassified by clinical assessment alone, making objective biochemical markers essential 1