What tests should be done for a patient complaining of abdominal pain?

Diagnostic Approach to Abdominal Pain

For a patient complaining of abdominal pain, laboratory tests including full blood count, electrolytes, liver enzymes, inflammatory biomarkers (ESR and CRP), and serum albumin should be performed, followed by appropriate imaging based on pain location, with CT being the preferred modality for most cases of acute abdominal pain when serious pathology is suspected. 1, 2

Initial Laboratory Evaluation

Essential Laboratory Tests:

• Complete blood count (to assess for anemia, leukocytosis, thrombocytosis)
• Serum electrolytes
• Liver enzymes
• Inflammatory markers:
  • C-reactive protein (CRP)
  • Erythrocyte sedimentation rate (ESR)
• Serum albumin and pre-albumin (to assess nutritional status and inflammation)
• Renal function tests
• Fecal calprotectin (when possible)
• Stool cultures and Clostridium difficile toxin test (to rule out infectious causes) 1

Additional Tests Based on Clinical Suspicion:

• Pregnancy test for all women of reproductive age 1, 2
• Lipase/amylase (if pancreatitis suspected)
• Urinalysis (if urinary tract pathology suspected)
• Lactate and arterial blood gas (if mesenteric ischemia suspected) 1, 2

Imaging Selection Based on Pain Location

Right Upper Quadrant Pain:

• First-line: Ultrasonography of abdomen
• Second-line: CT with contrast if ultrasound is equivocal 1, 2

Right or Left Lower Quadrant Pain:

• First-line: CT of abdomen and pelvis with contrast media
• Alternative: Ultrasonography in pregnant patients or young women 1, 2

Diffuse or Non-localized Pain:

• First-line: CT of abdomen and pelvis with contrast media
• Alternative: Plain radiographs if CT is not immediately available (though limited diagnostic value) 1, 2

Special Considerations:

• Suspected appendicitis: Helical CT with intravenous contrast (no oral contrast required) 1
• Suspected mesenteric ischemia: CT angiography of abdomen with contrast 1
• Suspected cholecystitis: Ultrasonography (may consider cholescintigraphy or CT if ultrasound is equivocal) 1
• Suspected small bowel obstruction: CT with contrast (conventional radiography may be appropriate for initial evaluation) 1

Special Patient Populations

Pregnant Patients:

• Ultrasound as first imaging modality
• MRI if ultrasound is inconclusive (avoid ionizing radiation) 1, 2

Women of Reproductive Age:

• Always perform pregnancy test before imaging 1, 2
• Consider transvaginal ultrasound for gynecological causes 2

Elderly Patients:

• Higher index of suspicion for mesenteric ischemia, diverticulitis, and bowel obstruction
• Often present with atypical symptoms 2
• CT imaging should be obtained more readily due to higher risk of serious pathology

Common Pitfalls to Avoid

1. Relying solely on laboratory tests without appropriate imaging
2. Dismissing pain as functional without adequate workup
3. Administering antibiotics without evidence of infection
4. Delaying imaging in patients with significant pain
5. Failing to consider extra-abdominal causes of pain (e.g., pneumonia, myocardial infarction)
6. Overlooking gynecological causes in women 2
7. Not performing Carnett's test to differentiate abdominal wall pain from intra-abdominal pain 3

Red Flags Requiring Immediate Attention

• Pain out of proportion to physical examination (suggests mesenteric ischemia) 1
• Unexplained weight loss
• Persistent fever
• Pain waking patient from sleep
• Abdominal distension with sudden onset 2

By following this systematic approach to laboratory testing and imaging based on pain location and clinical presentation, clinicians can efficiently diagnose the cause of abdominal pain and provide appropriate treatment, ultimately improving patient outcomes in terms of morbidity, mortality, and quality of life.