What is the differential diagnosis for a female patient with lower abdominal pain, elevated CRP, elevated WCC, hypokalemia, and a non-diagnostic CT abdomen and pelvis?

Differential Diagnosis for Lower Abdominal Pain with Elevated Inflammatory Markers and Normal CT

Despite a normal CT abdomen/pelvis, the combination of lower abdominal pain, significantly elevated CRP (165), leukocytosis (WCC 17), and hypokalemia in a female patient most likely represents either early/evolving intra-abdominal pathology not yet visible on CT, pelvic inflammatory disease, or a non-visualized gynecologic process requiring transvaginal ultrasound.

Primary Diagnostic Considerations

Gynecologic Pathology (Most Critical to Exclude)

• Pelvic inflammatory disease (PID) is a leading consideration given that CT has limited sensitivity for early tubal inflammation, and this diagnosis increased by 280% following CT in patients with fever and abdominal complaints 1
• Ovarian torsion must be urgently excluded as it can present with intermittent pain and may not show definitive findings on standard CT, requiring transvaginal ultrasound for diagnosis 2
• Tubo-ovarian abscess or pyosalpinx may be present but not adequately visualized without dedicated pelvic imaging 2
• Transvaginal ultrasound is essential as the next diagnostic step in reproductive-age women with lower abdominal pain when CT is non-diagnostic, as it has superior sensitivity for ovarian and tubal pathology 2

Early or Evolving Inflammatory Conditions

• Appendicitis cannot be completely excluded despite normal CT, as sensitivity is 95% (meaning 5% are missed), particularly in early presentations 1, 3
• Diverticulitis may be present but not yet showing typical CT findings in very early stages, though CT typically has high accuracy for this diagnosis 1
• Smoldering diverticulitis represents a distinct entity with persistent abdominal pain and continued inflammation on imaging, occurring in approximately 5% of patients after acute diverticulitis 1
• Inflammatory bowel disease (Crohn's disease) can present with elevated inflammatory markers and may show only subtle findings or be CT-negative in early mucosal disease 1

Infectious/Inflammatory Causes

• Infectious enterocolitis can cause significant inflammatory marker elevation with initially normal CT findings 3
• Pseudomembranous (C. difficile) colitis shows CT findings in only 88% of cases, meaning 12% may have normal initial imaging 1
• Mesenteric adenitis can mimic appendicitis with elevated inflammatory markers 4

Metabolic and Systemic Considerations

• The hypokalemia (K 3.0) suggests either significant gastrointestinal losses (vomiting, diarrhea) or may indicate a more systemic process 3
• Severe gastroenteritis remains possible despite elevated inflammatory markers, though the degree of CRP elevation (165) is unusually high for uncomplicated gastroenteritis 3

Critical Next Steps

Immediate Additional Workup Required

• Obtain β-hCG immediately in all reproductive-age women to exclude ectopic pregnancy, which is mandatory before further imaging decisions 2
• Perform transvaginal ultrasound urgently to evaluate for PID, ovarian torsion, tubo-ovarian abscess, or other gynecologic pathology not adequately assessed by CT 2
• Repeat inflammatory markers (CRP, WCC) in 12-24 hours if patient remains symptomatic, as evolving pathology may declare itself 5

Imaging Considerations

• MRI abdomen/pelvis without contrast may be considered if ultrasound is non-diagnostic and clinical suspicion remains high, as it has 100% sensitivity for appendicitis and can detect subtle inflammatory changes 1
• Consider repeat CT in 24-48 hours if symptoms progress or inflammatory markers worsen, as early pathology may become visible 1

Important Clinical Pitfalls

Common Diagnostic Errors to Avoid

• Do not assume normal CT excludes all pathology - CT sensitivity is not 100%, and early inflammatory processes may not yet show typical findings 1
• Never skip gynecologic evaluation in reproductive-age women - PID and ovarian pathology are frequently missed when relying solely on CT abdomen/pelvis 2
• The combination of normal WCC and CRP makes appendicitis unlikely, but this patient has ELEVATED markers - no patients with both normal WCC and CRP had appendicitis in one study, but this patient has both elevated 5
• Hypokalemia should not be dismissed - it may indicate significant fluid/electrolyte losses suggesting more severe pathology than initially apparent 3

When to Escalate Care

• Surgical consultation is warranted if symptoms worsen, peritoneal signs develop, or repeat imaging shows evolving pathology 1
• Gynecology consultation should be obtained urgently if transvaginal ultrasound suggests PID, TOA, or ovarian torsion 2
• Consider empiric antibiotic therapy for suspected PID while awaiting definitive diagnosis, as delay in treatment worsens outcomes 2