What is the approach for evaluating abdominal pain?

Evaluation of Abdominal Pain

CT of the abdomen and pelvis with IV contrast is the preferred initial imaging study for acute nonlocalized abdominal pain, as it changes the leading diagnosis in 51% of patients and alters admission decisions in 25% of cases. 1

Initial Clinical Assessment

Begin by determining the exact location of pain, as this fundamentally guides your diagnostic and imaging approach:

• Right upper quadrant pain: Suspect acute cholecystitis, hepatobiliary disease, or cholangitis 1
• Right lower quadrant pain: Appendicitis is the critical diagnosis to exclude; also consider ectopic pregnancy in women of reproductive age 2
• Left lower quadrant pain: Diverticulitis is the leading consideration in older adults; consider sigmoid volvulus with chronic constipation history 2
• Epigastric pain: Consider peptic ulcer disease, gastritis, or acute pancreatitis 2

Assess vital signs specifically for these red flags:

• Tachycardia is the most sensitive early warning sign of surgical complications and should trigger urgent investigation even before other symptoms develop 3
• Fever with tachycardia and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis 3
• Hypotension suggests bleeding or sepsis requiring immediate intervention 3

Examine for peritoneal signs that indicate surgical emergencies:

• Rigid abdomen or rebound tenderness indicates perforation or ischemia 2
• Pain out of proportion to physical findings strongly suggests mesenteric ischemia 3, 2
• Abdominal distension with vomiting indicates bowel obstruction 2

Laboratory Evaluation

Order these initial tests for all patients with acute abdominal pain:

• Complete blood count (CBC) to assess for leukocytosis indicating infection or inflammation 3, 4
• Comprehensive metabolic panel (CMP) including liver function tests (ALT, AST, alkaline phosphatase, bilirubin) to evaluate hepatobiliary pathology 4
• Serum lipase (more specific than amylase) for suspected pancreatitis 4
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 4
• Beta-hCG testing is mandatory in all women of reproductive age before proceeding with imaging to rule out ectopic pregnancy 3, 4, 2

Advanced laboratory markers when specific conditions are suspected:

• C-reactive protein (CRP) has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease; elevated CRP (OR = 6.24) is a significant predictor of hospital admission 3
• Lactate and D-dimer if mesenteric ischemia is suspected, though normal lactate does not exclude internal herniation or early ischemia 3, 4
• Blood cultures if sepsis is suspected, especially in immunocompromised patients 4

Imaging Strategy by Pain Location

Right upper quadrant pain:

• Ultrasonography is the initial imaging test of choice for evaluating acute cholecystitis and hepatobiliary disease 1, 4

Right lower quadrant pain:

• CT of the abdomen and pelvis with contrast is the initial imaging study of choice for suspected appendicitis 1, 4
• Ultrasound may be considered first in young patients to minimize radiation exposure before proceeding to CT 1

Left lower quadrant pain:

• CT of the abdomen and pelvis with contrast is recommended, especially for suspected diverticulitis 1, 3

Nonlocalized or diffuse abdominal pain:

• CT of the abdomen and pelvis with IV contrast is the preferred imaging option due to the broad differential diagnosis and need for rapid imaging 1
• CT changes the leading diagnosis in 49-51% of patients and alters surgical plans in 25% 1
• Most institutions do not routinely use oral contrast due to delays in scan acquisition without clear diagnostic advantage 1

Special imaging considerations:

• Non-contrast CT for suspected kidney stones 3
• CT angiography for suspected mesenteric ischemia 3

Critical Pitfalls to Avoid

Failing to obtain β-hCG testing in women of reproductive age before imaging can delay diagnosis of ectopic pregnancy, which is a life-threatening condition 2

Conventional radiography has limited diagnostic value in most patients with abdominal pain and should not be routinely ordered; it has only 49% sensitivity for bowel obstruction and low sensitivity for sources of fever or abscess 1, 4

Do not dismiss atypical presentations in elderly patients, as they may have normal laboratory values despite serious infection and are at higher risk for malignancy, diverticulitis, and vascular causes 1, 2

In post-bariatric surgery patients, classic peritoneal signs are often absent, and tachycardia is the most critical warning sign; consider internal herniation even with normal lactate 3

Over-relying on normal laboratory values early in disease progression can lead to missed diagnoses, particularly in mesenteric ischemia where lactate may initially be normal 3, 2

Special Population Considerations

Women of reproductive age: Always consider gynecologic conditions including ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease; CT of the abdomen and pelvis with contrast is most appropriate for pelvic pain 3, 2

Elderly patients: Symptoms may be atypical and require more thorough evaluation even if laboratory tests are normal; they have higher likelihood of malignancy, diverticulitis, and vascular causes 1, 2

Immunocompromised patients: Typical signs of abdominal sepsis may be masked, diagnosis may be delayed, and mortality rate is high; a more extensive workup is necessary 1, 4