What is the initial assessment and management for an adult presenting with abdominal pain, including red‑flag identification, work‑up, and supportive treatment?

Initial Assessment and Management of Acute Abdominal Pain in Adults

For an adult presenting with acute abdominal pain, immediately assess vital signs and red-flag features, obtain targeted laboratory tests including CBC and beta-hCG in women of childbearing age, and proceed directly to CT abdomen/pelvis with IV contrast for nonlocalized pain or when serious pathology is suspected. 1

Immediate Red-Flag Identification

Recognize life-threatening conditions that require urgent intervention:

• Tachycardia is the single most sensitive early warning sign of surgical complications and should trigger immediate investigation even before other symptoms develop 1, 2
• Severe pain out of proportion to physical examination findings indicates mesenteric ischemia until proven otherwise 1, 3
• Sudden onset severe pain with hypotension suggests ruptured abdominal aortic aneurysm (mortality >50%) 3
• Signs of peritonitis (rigid abdomen, rebound tenderness, guarding) require urgent surgical evaluation 1, 3
• The triad of fever, tachycardia, and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis 1
• Hemodynamic instability (hypotension, tachycardia, tachypnea) indicates bleeding or sepsis 1, 3
• Abdominal distension with vomiting suggests bowel obstruction 1, 3

Essential Laboratory Tests

Obtain these tests immediately upon presentation:

• Complete blood count (CBC) to evaluate for leukocytosis indicating infection or inflammation 1, 2
• Beta-hCG test in ALL women of childbearing age before any imaging to rule out ectopic pregnancy 1, 2
• Elevated C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease 1, 2
• Elevated lactate suggests ischemia or sepsis, though normal levels do not exclude early ischemia 1, 2
• Metabolic panel, liver function tests, amylase, and lipase for suspected pancreatitis or hepatobiliary disease 1, 2
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 2

Critical caveat: Normal laboratory values early in disease do not exclude serious pathology, especially in elderly patients 1

Imaging Strategy Based on Clinical Presentation

For Nonlocalized or Diffuse Abdominal Pain:

CT abdomen and pelvis with IV contrast is the optimal initial imaging study 4, 1, 2. This approach:

• Alters diagnosis in 49% of patients and changes management in 42% of cases 4, 2
• Has sensitivity >95% for detecting appendicitis, diverticulitis, and complications such as abscess or perforation 3, 2
• Provides comprehensive evaluation of all abdominal organs in a single examination 3

Avoid conventional radiographs as they have limited diagnostic value in most patients with acute abdominal pain 4, 1, 3

For Localized Pain:

• Right lower quadrant pain: Abdominal ultrasound is the initial imaging method 1
• Right upper quadrant pain (suspected biliary disease): Ultrasound is the test of choice 1, 3
• Pelvic pain: CT abdomen/pelvis with contrast 1
• Left lower quadrant pain (suspected diverticulitis): CT abdomen/pelvis with contrast 1

Special Imaging Considerations:

• Suspected mesenteric ischemia: CT angiography is the gold standard 1, 3
• Suspected kidney stones: Non-contrast CT abdomen/pelvis 1
• Pregnant patients: Use ultrasound first; if negative or equivocal, proceed to MRI (not CT) to avoid radiation 2

Supportive Treatment

Fluid Resuscitation and Electrolyte Management:

• Administer adequate volume of intravenous fluids to all patients presenting with acute abdomen 4
• Correct electrolyte abnormalities and anemia 4

Thromboprophylaxis:

• Provide low molecular weight heparin for thromboprophylaxis in all patients with acute abdomen 4

Antibiotic Therapy:

• Do NOT routinely administer antibiotics unless superinfection is suspected or intra-abdominal abscess is present 4
• When indicated, use broad-spectrum coverage against Gram-negative/aerobic bacilli, Gram-positive streptococci, and obligate anaerobic bacilli 4
• Appropriate regimens include fluoroquinolones or third-generation cephalosporin plus metronidazole 4
• Clinical improvement should occur within 3-5 days of starting antibiotics; if not, re-evaluate with repeat imaging 4

Pain Management:

Early administration of analgesia reduces patient discomfort without impairing diagnostic accuracy and is recommended 5. However, use judicious dosing as the impact on diagnostic accuracy depends on dosage and route of administration 5.

Special Population Considerations

Elderly Patients:

• May present with atypical symptoms and require more thorough evaluation even with normal laboratory tests 1, 2
• Have higher likelihood of malignancy, diverticulitis, and vascular causes 1, 2

Post-Bariatric Surgery Patients:

• Often present with atypical symptoms; tachycardia is the most critical warning sign 1, 3
• Classic peritoneal signs are often absent 1
• Consider internal herniation even with normal lactate 1

Immunocompromised Patients:

• May have masked signs of abdominal sepsis with delayed diagnosis resulting in high mortality 1

Women of Reproductive Age:

• Always consider gynecologic conditions including ectopic pregnancy, ovarian torsion, and pelvic inflammatory disease 1, 2

Critical Pitfalls to Avoid

• Do not rely on normal laboratory values to exclude serious disease, especially early in presentation or in elderly patients 1, 2
• Do not assume negative ultrasound rules out severe pathology—proceed to CT if clinical suspicion persists 3
• Do not delay CT in patients with clinical deterioration while performing additional non-diagnostic tests 3
• Do not ignore tachycardia as an early warning sign, even before other symptoms develop 1, 2
• Do not routinely order plain radiographs as they have limited diagnostic value 4, 1, 3
• Scan the entire abdomen and pelvis rather than limiting coverage based on symptoms—limited scanning visualized all acute pathology in only 33% of abnormal cases 2

Multidisciplinary Approach

Optimal management involves collaboration between gastroenterologist and acute care surgeon for all patients with acute abdomen 4. This ensures timely surgical consultation when indicated and appropriate medical management when surgery is not immediately required.