What clinical tests are indicated for evaluating an adult with suspected acute abdomen?

Clinical Tests for Acute Abdomen

For adults with acute abdomen, obtain laboratory markers of inflammation (complete blood count, C-reactive protein) and organ-specific tests (hepatobiliary markers, lipase, urinalysis, pregnancy test in women of reproductive age), followed by imaging based on pain location—with CT abdomen/pelvis with IV contrast as the primary modality for most presentations, except right upper quadrant pain where ultrasound is preferred. 1, 2

Laboratory Testing

Essential Initial Labs

• Complete blood count (CBC) - assess for leukocytosis indicating infection/inflammation
• C-reactive protein (CRP) - inflammatory marker, though CRP and WBC alone are insufficient to discriminate urgent from non-urgent causes 3
• Hepatobiliary markers - for suspected biliary pathology
• Lipase - for suspected pancreatitis
• Urinalysis - for urinary tract pathology
• Electrolytes, creatinine, glucose - baseline metabolic assessment 2
• Pregnancy test (beta-hCG) - mandatory in all women of reproductive age before imaging 4, 2

Blood Cultures - Limited Role

Do not routinely obtain blood cultures in non-immunocompromised patients with suspected intra-abdominal infection who have normal/elevated temperature without hypotension, tachypnea, or delirium, unless there is concern for antibiotic-resistant organisms 1

Imaging Studies by Clinical Presentation

Right Upper Quadrant Pain

Abdominal ultrasound is the initial imaging modality for suspected acute cholecystitis or cholangitis 1, 4

• If ultrasound is inconclusive, proceed to CT with IV contrast, MRI/MRCP, or HIDA scan 1
• Diagnosis requires clinical signs (jaundice, fever, RUQ pain), laboratory findings (inflammation markers, biliary stasis indicators), and imaging findings (biliary dilatation, stones, strictures) 1

Right Lower Quadrant Pain (Suspected Appendicitis)

Non-pregnant adults: Obtain abdominal CT with IV contrast as initial imaging 1

• CT without IV contrast also has high diagnostic accuracy and may be appropriate 1
• Ultrasound or MRI are reasonably accurate alternatives depending on patient circumstances 1
• If CT is negative but suspicion persists: observe with supportive care ± antibiotics; if suspicion is high, consider surgical intervention 1

Pregnant patients: Start with abdominal ultrasound; if equivocal, proceed to MRI (preferred over CT when available) 1, 2

Children/adolescents: Start with abdominal ultrasound; if equivocal, proceed to MRI or CT 1

Lower Abdominal Pain (Suspected Diverticulitis)

Abdominal CT with IV contrast is the initial diagnostic modality 1, 4

• IV contrast helps characterize bowel wall abnormalities and detect complications
• CT without IV contrast may be appropriate in select cases 1
• If CT unavailable or contraindicated: ultrasound or MRI are alternatives 1
• Pregnant patients: Ultrasound or MRI can be considered (no clear preference established) 1

Suspected Intra-Abdominal Abscess

Non-pregnant adults/adolescents: Obtain abdominal CT scan as initial imaging 1

• Use IV contrast to improve visualization of abscess wall 1
• Additional imaging beyond CT usually not necessary due to high accuracy 1

Children: Start with abdominal ultrasound as initial imaging 1

• MRI is a reasonable alternative if readily available 1
• Balance radiation exposure (CT) against operator-dependence (ultrasound) and availability/sedation needs (MRI) 1

Risk Stratification

For adults with complicated intra-abdominal infection requiring severity assessment, use APACHE II score within 24 hours of hospitalization or ICU admission 1

• World Society of Emergency Surgery Sepsis Severity Score is an acceptable alternative 1
• No validated pediatric-specific scoring system currently recommended 1

Key Clinical Pitfalls

1. Conventional radiography has limited diagnostic value in acute abdomen—no place in modern work-up due to lack of added value beyond clinical assessment 4, 3

2. Clinical evaluation alone is insufficient for definitive diagnosis but can discriminate urgent from non-urgent causes 3. Studies show clinical diagnosis accuracy of only 94%, X-ray 40%, ultrasound 52% 5

3. Ultrasound limitations: Operator-dependent and can yield equivocal results, particularly for appendicitis where diagnostic agreement is low 1, 6

4. CT accuracy advantage: Because of CT's high accuracy, immediate additional imaging beyond CT is usually unnecessary 1

5. Step-by-step approach is efficient: Advanced diagnostics unnecessary in 80% of cases, except for conditions requiring disease staging (pancreatitis, diverticulitis) where advanced imaging should be pursued from onset 7