What is the main diagnosis and treatment approach for a patient presenting with abdominal pain?

Acute Abdominal Pain: Diagnosis and Treatment

The main diagnosis depends on pain location and clinical presentation, with appendicitis (15.9-28.1% of surgical cases) and nonspecific abdominal pain (30-41%) being most common, requiring a structured approach prioritizing vital sign assessment, location-based imaging, and recognition of surgical emergencies. 1, 2

Initial Clinical Assessment Priority

Tachycardia is the single most sensitive early warning sign of surgical complications and should trigger urgent investigation immediately, even before other symptoms develop. 1 The combination of fever, tachycardia, and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis. 1

Critical Vital Sign Evaluation

• Assess for tachycardia first as the most sensitive indicator of surgical disease 1
• Evaluate for fever, hypotension, or tachypnea indicating infection, bleeding, or complications 1
• Look for signs of peritonitis (rigid abdomen, rebound tenderness) requiring urgent evaluation 1

Red Flags Requiring Immediate Action

• Severe pain out of proportion to physical findings suggests mesenteric ischemia 1
• Hemodynamic instability suggests bleeding or sepsis 1
• Abdominal distension with vomiting suggests bowel obstruction 1
• Positive Murphy's sign indicates acute cholecystitis 1

Mandatory Laboratory Testing

Every patient requires CBC, comprehensive metabolic panel, urinalysis, serum lipase, and β-hCG in all women of childbearing age before any imaging. 3, 4

Initial Laboratory Panel

• Complete blood count: High C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease 1
• Comprehensive metabolic panel including liver function tests for hepatobiliary pathology 3, 4
• Serum lipase (more specific than amylase for pancreatitis) 3, 4
• β-hCG testing is mandatory in all women of reproductive age to rule out ectopic pregnancy 1, 3, 4
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 3, 4

Additional Tests Based on Clinical Suspicion

• Elevated lactate suggests ischemia or sepsis, though normal levels do not exclude internal herniation or early ischemia 1
• Blood cultures if fever present and sepsis suspected 4
• Procalcitonin for assessing inflammatory response in suspected sepsis 1
• D-dimer and lactate if mesenteric ischemia suspected 1, 3

Location-Based Imaging Algorithm

The location of pain determines the appropriate initial imaging method. 1, 5

Right Upper Quadrant Pain

• Abdominal ultrasound is the first-line imaging for right upper quadrant pain 1
• Obtain liver function tests and hepatobiliary markers 3, 4
• Suspected diagnosis: acute cholecystitis 1

Right Lower Quadrant Pain

• Abdominal ultrasound is the most appropriate initial imaging for acute right lower quadrant pain 1
• Consider ultrasound before CT to minimize radiation exposure, especially in young patients 1
• If ultrasound inconclusive, proceed to CT abdomen/pelvis with contrast 1
• Suspected diagnosis: acute appendicitis (15.9-28.1% of surgical cases) 1

Left Lower Quadrant Pain

• CT abdomen/pelvis with contrast is recommended, especially for suspected diverticulitis 1

Pelvic Pain

• CT abdomen/pelvis with contrast is the most appropriate initial imaging 1
• Consider gynecologic conditions (ectopic pregnancy, ovarian torsion, pelvic inflammatory disease) in women of childbearing age 1

Nonspecific or Diffuse Abdominal Pain

• CT abdomen/pelvis with contrast is the optimal choice, especially if fever or suspicion of serious illness 1

Epigastric Pain

• Consider upper GI series with fluoroscopy if gastritis, peptic ulcer disease, or GERD suspected 1

Diagnosis by Suspected Condition

Acute Appendicitis

• CT abdomen/pelvis with contrast is definitive imaging 1
• Frequency: 15.9-28.1% of cases requiring surgery 1

Acute Cholecystitis

• Abdominal ultrasound is the imaging of choice 1

Kidney Stones

• Non-contrast CT abdomen/pelvis is recommended 1

Bowel Obstruction

• CT abdomen/pelvis with contrast is recommended 1
• Accounts for 15% of acute abdominal pain admissions 1
• Small bowel obstruction: most commonly caused by adhesions, hernias, and neoplasms 1
• Large bowel obstruction: most commonly caused by cancer, volvulus, and diverticular disease 1

Mesenteric Ischemia

• CT angiography of the abdomen is recommended 1
• Suspect when severe pain is out of proportion to physical findings 1

Treatment Approach

General Management Principles

All patients presenting with acute abdomen should receive adequate intravenous fluids, low molecular weight heparin for thromboprophylaxis, and correction of electrolyte abnormalities and anemia. 6

Antibiotic Therapy

• Antibiotics should not be routinely administered, but only if superinfection is considered and in the presence of intra-abdominal abscess 6
• When indicated, use antimicrobial therapy against Gram-negative/aerobic and facultative bacilli, Gram-positive streptococci, and obligate anaerobic bacilli 6
• Combination of fluoroquinolones or third-generation cephalosporin and metronidazole is appropriate for intra-abdominal infections 6
• Clinical improvement should be seen within 3-5 days after starting antibiotics 6

Multidisciplinary Management

Optimal management requires multidisciplinary involvement of gastroenterologist and acute care surgeon. 6

Special Population Considerations

Elderly Patients

• Higher likelihood of malignancy, diverticulitis, and vascular causes 1
• Symptoms may be atypical and require more thorough evaluation, even if laboratory tests are normal 1

Post-Bariatric Surgery Patients

• Often present with atypical symptoms 1
• Tachycardia is the most critical warning sign 1
• Classic peritoneal signs are often absent 1
• Consider internal herniation even with normal lactate 1

Women of Childbearing Age

• Mandatory β-hCG testing before imaging 1, 3, 4
• Consider ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease 1

Critical Pitfalls to Avoid

• Failing to obtain pregnancy testing in women of reproductive age before imaging can lead to delayed diagnosis of pregnancy-related conditions 3, 4
• Over-reliance on laboratory tests alone can lead to missed diagnoses, as early laboratory findings may be of little value 4
• Avoiding overuse of CT scans to minimize ionizing radiation exposure, especially in young patients 1
• Normal lactate does not exclude internal herniation or early ischemia 1
• Normal CRP does not exclude complications 1

Timing and Urgency

For every elapsed hour until specific treatment is provided, mortality rises. 2 The acute abdomen carries 2-12% mortality overall. 2 If a patient's condition does not improve within 3-5 days after starting treatment, re-evaluation and repeat imaging are indicated. 6