What is the appropriate workup for a 40-year-old patient presenting with lower abdominal pain?

Workup for Lower Abdominal Pain in a 40-Year-Old Patient

CT abdomen and pelvis with IV contrast is the most appropriate initial imaging study for a 40-year-old patient presenting with lower abdominal pain, as it is the most accurate examination that guides appropriate management regardless of patient sex or body habitus. 1

Initial Clinical Assessment

Immediate Evaluation

• Assess hemodynamic stability first: Check for tachycardia, hypotension, fever, or signs of shock, which indicate potential bowel ischemia, perforation, or sepsis requiring emergency intervention 2
• Examine for peritoneal signs: Look for guarding, rebound tenderness, and rigidity, which suggest perforation or ischemia and mandate urgent surgical consultation 2
• Evaluate for obstruction: Abdominal distension has a positive likelihood ratio of 16.8 for bowel obstruction; assess for colicky pain, vomiting, and absence of flatus 2

Key Differential Diagnoses at Age 40

• Diverticulitis is increasingly common, as approximately 10% of the Western population has diverticulosis at 40 years of age, with 5-25% developing diverticulitis 1
• Other common causes include colitis, inflammatory bowel disease, epiploic appendagitis, bowel obstruction, hernia, ovarian and fallopian tube pathology (in females), pyelonephritis, and urolithiasis 1
• Appendicitis remains in the differential, with odds ratio of colon cancer increasing 38.5-fold in patients over 40 presenting with acute appendicitis 1

Essential Laboratory Testing

Mandatory Initial Labs

• Complete blood count (CBC): Leukocytosis >14,000 suggests infection, ischemia, or inflammation; marked elevation indicates potential bowel ischemia 2
• Metabolic panel: Low bicarbonate, elevated lactate, and elevated pH indicate intestinal ischemia 2
• C-reactive protein (CRP): Helps identify infection or inflammation 3, 4
• Urinalysis: Evaluates for urinary tract infection or kidney stones; hematuria indicates urolithiasis and pyuria suggests infection 3
• Pregnancy test: Mandatory in all women of reproductive age before imaging, even at age 40 if any possibility of pregnancy exists 2
• Lipase and hepatobiliary markers: Consider based on pain location and clinical suspicion 4

Imaging Algorithm

Primary Imaging Recommendation

CT abdomen and pelvis with IV contrast is rated as "usually appropriate" (rating 8/9) for nonspecific lower abdominal pain 1, 3

Advantages of CT with IV Contrast:

• Highly accurate for detecting diverticulitis, appendicitis (>95% sensitivity), kidney stones, abscesses, and bowel pathology 2, 3
• Changes diagnosis in 49% of cases and management in 42% of patients with nonspecific pain 2
• Sensitive for small quantities of extraluminal air, indicating luminal perforation with surgical implications 1
• Effective regardless of patient sex or body habitus 1

Alternative Imaging (When CT with IV Contrast Unavailable)

• Ultrasound, MRI, or CT without IV contrast should be used in patients with severe kidney disease or contrast allergy, according to resource availability 1, 3
• Ultrasonography is preferred for right upper quadrant pain (81% sensitivity and 83% specificity for cholecystitis) 2

Critical Pitfalls to Avoid

Common Diagnostic Errors

• Do not rely on normal laboratory values alone: Many serious infections present with normal white blood cell counts, especially in older patients 2
• Do not delay imaging based on clinical impression: CT changes diagnosis in approximately 50% of cases with nonspecific pain 2
• Do not overlook malignancy: The odds ratio of colon cancer increases 38.5-fold in patients over 40 with acute appendicitis 1
• Do not forget pregnancy testing: Even in perimenopausal women, missing ectopic pregnancy can have catastrophic consequences 2
• Do not assume diverticulitis based on classic triad alone: The classic triad (left lower quadrant pain, fever, leukocytosis) is present in only 25% of patients 3

Follow-Up Considerations for Age 40

Colonoscopy Indications

• Colonic screening is strongly recommended for patients ≥40 years old with complicated appendicitis treated non-operatively or operatively 1
• Colonoscopy should be performed if the patient has not yet undergone age-appropriate colon cancer screening, has abnormal pericolic lymph nodes, has a luminal colon mass, or has an uncertain diagnosis 1
• The incidence of appendicular neoplasms is 3-17% in adult patients ≥40 years old with complicated appendicitis 1