In a 61-year-old woman with a three-year history of chronic left lower-quadrant abdominal pain, nausea, constipation, and previously normal fecal immunochemical test, abdominal ultrasound, celiac serology, H. pylori testing, and routine laboratory studies, what additional investigations or laboratory tests should be pursued?

Chronic Left Lower Quadrant Pain: Next Steps After Negative Initial Workup

Immediate Next Investigation

Order a CT abdomen and pelvis with IV contrast as the definitive next step, as it provides approximately 98% diagnostic accuracy and will identify structural pathology that ultrasound may have missed. 1, 2, 3

Why CT is Essential in This Case

Your patient has had three years of symptoms with only basic imaging (ultrasound). The American College of Radiology rates CT abdomen/pelvis with IV contrast as 8/9 (usually appropriate) for left lower quadrant pain and explicitly states that clinical assessment alone misclassifies pathology in 34-68% of cases. 2, 3

Key benefits of CT with IV contrast in this scenario:

• Detects diverticulitis, early malignancy, inflammatory bowel disease, and other structural causes that ultrasound cannot reliably identify 1, 2
• Identifies pericolonic lymphadenopathy >1 cm, which suggests malignancy rather than benign disease 1
• Evaluates for complications like abscess, fistula, or bowel obstruction 2
• Reduces hospital admissions by >50% through accurate risk stratification 2

Critical Laboratory Tests to Order Now

Before or alongside CT imaging, obtain:

Complete blood count with differential:

• A left shift ≥75% neutrophils suggests bacterial infection 3
• Anemia may indicate chronic GI bleeding from malignancy or inflammatory bowel disease 3

C-reactive protein (CRP):

• CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity and 91.1% specificity 3
• When CRP >50 mg/L is combined with left lower quadrant tenderness and absence of vomiting, diagnostic accuracy for diverticulitis reaches 97% 3

Lactate level:

• Elevated lactate signals sepsis and metabolic derangement if the patient appears systemically ill 3

β-hCG:

• Mandatory in all women of reproductive age before CT imaging to exclude ectopic pregnancy 3

Additional Considerations for Gynecologic Causes

Given her age (61), consider pelvic/transvaginal ultrasound if not already performed adequately:

• The American College of Radiology recommends evaluating gynecologic causes in women with left lower quadrant pain 1
• Cyclical pain patterns suggest gynecologic etiology requiring pelvic ultrasound 1
• Even postmenopausal women can have ovarian pathology causing chronic pain 1

Red Flags That Would Change Management Urgency

Watch for these features that mandate immediate emergency evaluation:

• Fever, inability to pass gas/stool, severe tenderness with guarding, vomiting, bloody stools, or signs of shock 1
• Weight loss or change in bowel habits warrant repeat colonoscopy despite prior normal study 1
• New pericolonic lymphadenopathy >1 cm on imaging suggests malignancy 1

If CT and Labs Are Normal: Consider Functional Disorder

Only after structural pathology is definitively excluded by CT should you consider irritable bowel syndrome (IBS):

• The diagnosis of functional bowel disorder always presumes absence of structural or biochemical explanation 4
• Pain related to bowel movements or dietary triggers points toward IBS 1
• For constipation-predominant symptoms, a therapeutic trial of fiber may be sufficient if imaging is negative 4
• For pain-predominant symptoms, a plain abdominal radiograph during acute episodes to exclude obstruction, followed by antispasmodic trial if negative 4

Gastroenterology Referral Timing

Refer to gastroenterology:

• If CT reveals any structural abnormality requiring specialist management 1
• If symptoms persist despite conservative measures and negative imaging, for functional bowel disorder management 1
• For consideration of colonoscopy if not done recently, given her age and chronic symptoms 4

Critical Pitfall to Avoid

Do not diagnose IBS or functional disorder without CT imaging in a 61-year-old woman with three years of progressive symptoms. The American College of Radiology states that functional bowel disorders become the most likely diagnosis only when structural pathology has been excluded by CT and colonoscopy. 1 Your patient's age (>50 years) and symptom duration mandate ruling out malignancy, diverticular disease, and inflammatory conditions before attributing symptoms to a functional disorder. 4, 1