What investigations are needed for a patient with suspected intra-abdominal infection or acute cholangitis?

Diagnostic Workup for Suspected Intra-Abdominal Infection or Acute Cholangitis

Begin with abdominal ultrasound as the first-line imaging modality for suspected acute cholecystitis or cholangitis, followed by laboratory assessment of liver function tests and inflammatory markers, with blood and bile cultures to guide antimicrobial therapy. 1

Initial Clinical Assessment

Key Clinical Features to Document

• Charcot's triad: Right upper quadrant pain, fever, and jaundice (present in acute cholangitis) 1, 2
• Reynolds pentad: Addition of altered mental status and hypotension to Charcot's triad indicates severe disease 2, 3
• Murphy's sign: Tenderness with palpation over the gallbladder 1
• Assess for signs of systemic illness: fever, chills, abdominal distention, nausea, vomiting 1

Laboratory Investigations

Essential Blood Tests

• Liver function panel: Direct and indirect bilirubin, AST, ALT, alkaline phosphatase (ALP), GGT, and albumin 1
• Inflammatory markers: Complete blood count, C-reactive protein (CRP), procalcitonin (PCT) 1
• Lactate levels: In critically ill patients to assess severity of sepsis 1
• Blood cultures: Obtain before initiating antibiotics (positive in approximately 40% of acute cholangitis cases) 4

These laboratory findings help establish indicators of inflammation and biliary stasis, which are essential diagnostic criteria for acute cholangitis 1

Imaging Studies

First-Line Imaging: Abdominal Ultrasound

Ultrasound is the initial imaging modality of choice for all non-pregnant adults and children with suspected acute cholecystitis or cholangitis. 1

Key ultrasound findings to identify:

• Gallstones (detected in ~98% of cases) 1
• Thickened gallbladder wall (>5mm) 1
• Pericholecystic fluid 1
• Biliary dilatation 1
• Ultrasonographic Murphy's sign (direct tenderness when probe pushed against gallbladder) 1

Advantages of ultrasound: No radiation exposure, readily available, portable, cost-effective, and provides timely results 1

Limitations: Operator-dependent, may be limited by patient obesity or abdominal tenderness 1

Subsequent Imaging if Ultrasound is Equivocal

For non-pregnant adults and children:

• CT with IV contrast as the next imaging modality to identify complications and rule out alternative diagnoses 1
• Consider risk-benefit ratio of radiation exposure, particularly in children 1

If CT is also equivocal and acute cholecystitis specifically is suspected:

• MRI/MRCP (Magnetic Resonance Cholangiopancreatography): Provides clearer visualization of surrounding structures, faster results, more readily available 1
• HIDA scan (Hepatobiliary Iminodiacetic Acid): Gold standard for diagnosing acute cholecystitis, less costly than MRI/MRCP, but requires several hours of fasting 1

For pregnant patients:

• Either ultrasound or MRI can be considered as initial imaging (avoid radiation exposure) 1

When to Obtain CT as Subsequent Imaging

CT with IV contrast should be obtained if complications are suspected: 1

• Biloma or intra-abdominal abscess
• Bile duct injury
• Hepatic or small bowel injury
• Retained stones in bile duct
• Hepatic abscess
• Portal vein thrombosis
• Acute biliary pancreatitis

Microbiological Workup

Culture Specimens

• Blood cultures: Obtain before antibiotic initiation 4
• Bile cultures: Essential for guiding targeted antimicrobial therapy, particularly in complicated cases 1, 5
• Infected fluid cultures: If percutaneous drainage or surgical intervention performed 1

Expected Pathogens

• Community-acquired infections: Gram-negative aerobes (Escherichia coli, Klebsiella pneumoniae) and anaerobes (Bacteroides fragilis) 5, 4
• Healthcare-associated infections: More resistant organisms including ESBL-producing Enterobacterales, MRSA, enterococci, and Candida species 1

Special Considerations

Healthcare-Associated Infections

For patients with previous biliary drainage, stenting, or nosocomial infection risk:

• Expect more resistant flora 1
• Tailor empiric antibiotics according to local hospital resistance patterns 1
• Obtain thorough microbiologic workup of infected fluid 1

Infection Exclusion

• Clostridium difficile testing: Particularly important in patients with colonic disease or recent antibiotic exposure 1
• Parasitic infections: If travel history suggests endemic area exposure, obtain stool examination for ova, cysts, and parasites 1

Postoperative Bile Duct Injury Surveillance

If bile duct injury is suspected postoperatively:

• Triphasic CT as first-line diagnostic imaging 1
• Complement with contrast-enhanced MRCP for exact visualization, localization, and classification of injury 1
• Percutaneous drainage of fluid collections if present 1

Diagnostic Criteria Summary for Acute Cholangitis

The diagnosis requires three components: 1

1. Clinical signs: Jaundice, fever, chills, and right upper quadrant abdominal pain
2. Laboratory findings: Indicators of inflammation and biliary stasis
3. Imaging findings: Biliary dilatation or evidence of etiology (stricture, stone, obstructing mass)