What are the initial laboratory tests and management for a patient presenting with abdominal pain?

Initial Laboratory Tests and Management for Abdominal Pain

The initial evaluation of a patient with abdominal pain should include complete blood count, comprehensive metabolic panel, urinalysis, and pregnancy test (for women of reproductive age), followed by targeted imaging based on pain location: ultrasonography for right upper quadrant pain and CT with contrast for right lower, left lower, or generalized abdominal pain. 1, 2

Initial Laboratory Tests

• Complete blood count (CBC) to evaluate for leukocytosis, which suggests infection or inflammation 1
• Comprehensive metabolic panel including liver function tests, especially for right upper quadrant pain 1
• C-reactive protein as a marker of inflammation 1
• Serum electrolytes, creatinine, and blood urea nitrogen to assess renal function 1
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 1
• Pregnancy test for all women of reproductive age before proceeding to imaging 1, 2
• Lactate levels to assess for bowel ischemia or severe sepsis 3, 2
• Blood cultures if fever is present 2

Imaging Studies Based on Pain Location

• Right upper quadrant pain: Ultrasonography is the initial imaging test of choice (sensitivity 81%, specificity 83% for cholecystitis) 3, 2
• Right lower quadrant pain (suspected appendicitis): CT with contrast media is recommended (sensitivity >95%) 3, 2
• Left lower quadrant pain (suspected diverticulitis): CT with contrast media is recommended 3, 2
• Diffuse/nonlocalized abdominal pain: CT of abdomen and pelvis with contrast media is typically the imaging modality of choice 3, 2
• Suspected kidney stones: Non-contrast CT of the abdomen and pelvis 2
• Plain radiographs have limited diagnostic value and should not be routinely used except in cases of suspected bowel obstruction 3

Initial Management Approach

• Hemodynamically unstable patients: Immediate resuscitation with intravenous fluids and surgical consultation 3, 1
• Signs of peritonitis or septic shock: Emergency surgical exploration 1
• Pain control: Appropriate analgesia should be provided and should not be withheld due to concerns about masking symptoms 1
• Fluid resuscitation: Crystalloid solutions should be the first choice for patients with signs of dehydration or sepsis 3
• Antibiotics: Not routinely administered but indicated for suspected infection or intra-abdominal abscess 1
• Suspected intra-abdominal abscesses >3cm: Consider percutaneous drainage with antimicrobial therapy 1

Special Considerations

• Elderly patients: Often present with atypical symptoms and may have normal laboratory tests despite serious pathology 1
• Women of childbearing age: Consider gynecologic conditions such as ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease 1
• Immunocompromised patients: May have masked signs of abdominal sepsis 1
• Pregnant patients: Ultrasound should be the first-line imaging, with MRI preferred over CT if additional imaging is needed 1
• Post-surgical patients: Perform CT as part of the workup if etiology is not readily identified 2

Common Pitfalls to Avoid

• Relying solely on laboratory tests without appropriate imaging 1
• Delaying surgical consultation in patients with peritonitis or signs of septic shock 1
• Overlooking gynecological causes in women of reproductive age 1
• Failing to recognize that elderly patients may present with atypical symptoms 1
• Overusing CT scans in young patients, increasing unnecessary radiation exposure 1
• Over-reliance on a single laboratory parameter, as no single test is sufficiently accurate to identify serious conditions like ischemic bowel 2