What is the likely diagnosis and management for a patient with left lower quadrant pain, sharp on palpation, and dull ache otherwise, with a soft abdomen elsewhere, normal observations, normal blood tests, and urine microscopy showing red blood cells (RBC) and leucocytes, awaiting abdominal ultrasound results?

Likely Diagnosis and Management of Left Lower Quadrant Pain with Urinary Findings

Order CT abdomen and pelvis with IV contrast immediately—this is the single most important diagnostic test to distinguish between urinary tract pathology (pyelonephritis, obstructive pyelonephritis, urolithiasis) and gastrointestinal causes (diverticulitis, colitis), with a diagnostic accuracy of 98%. 1, 2

Most Likely Diagnoses

The combination of left lower quadrant pain with RBCs and leucocytes in urine expands your differential significantly:

Urinary tract causes:

• Pyelonephritis or obstructive pyelonephritis - the presence of both RBCs and leucocytes strongly suggests urinary tract infection with possible obstruction 2
• Urolithiasis - kidney stones can cause both hematuria and secondary infection 2

Gastrointestinal causes:

• Acute diverticulitis - the most common cause of adult left lower quadrant pain, affecting 5-25% of patients with diverticulosis 1
• Epiploic appendagitis - presents with sharp, localized pain in well-appearing patients with minimal laboratory abnormalities 3, 4, 5
• Colitis or inflammatory bowel disease 1

Why CT with IV Contrast is Essential

CT with IV contrast is rated 8/9 (usually appropriate) by the American College of Radiology and provides: 1, 6

• Near 100% sensitivity for detecting urinary tract calculi 1
• 98% diagnostic accuracy for diverticulitis 1
• Detection of complications requiring urgent intervention (abscess, perforation, obstruction) 1, 2
• Identification of alternative diagnoses that present similarly 1, 6
• Guidance for treatment decisions (medical vs. surgical vs. interventional) 1, 6

Immediate Laboratory Tests to Order

While awaiting imaging results:

• Urine culture - to identify specific pathogen if UTI is present 2
• Complete blood count with differential - leukocytosis >15,000 with left shift suggests bacterial infection 2, 6
• C-reactive protein - CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity 2, 6
• Serum creatinine - to evaluate renal function, especially critical if obstruction is suspected 2

Management Algorithm Based on CT Findings

If Pyelonephritis or Obstructive Pyelonephritis:

• Uncomplicated pyelonephritis: Trimethoprim-sulfamethoxazole for 7-14 days 2
• Obstructive pyelonephritis: Immediate broad-spectrum IV antibiotics PLUS emergent decompression (ureteral stent or percutaneous nephrostomy) 2

If Uncomplicated Diverticulitis:

• Conservative management WITHOUT antibiotics is appropriate for immunocompetent patients 2, 6
• Antibiotics for maximum 7 days only if immunocompromised or elderly 2, 6

If Complicated Diverticulitis:

• Small abscess (<4 cm): Antibiotics alone for 7 days (Ertapenem 1g q24h or Eravacycline 1mg/kg q12h) 6
• Large abscess (≥4 cm): Percutaneous drainage PLUS antibiotics for 4 days 6
• Perforation with peritonitis: Emergency surgical consultation 6

If Epiploic Appendagitis:

• Conservative management with pain control—this is a self-limited condition that resolves without antibiotics or surgery 3, 4, 5
• Characteristic CT finding: focal area of soft-tissue attenuation with fat stranding along the colon wall 4, 5

Critical Red Flags Requiring Emergency Intervention

Immediate emergency evaluation is required if any of the following develop: 6

• Fever with inability to pass gas or stool
• Severe abdominal tenderness with guarding or rebound
• Vomiting or bloody stools
• Signs of shock (hypotension, tachycardia, altered mental status)
• Progressively worsening pain

Special Considerations

For premenopausal women: If gynecologic pathology is suspected, obtain pregnancy test first and consider pelvic/transvaginal ultrasound instead of or in addition to CT 1, 6

Common Pitfalls to Avoid

• Do not rely on clinical examination alone—misdiagnosis rates are 34-68% without imaging 1, 6
• Do not assume UTI explains everything—the combination of urinary findings with left lower quadrant pain requires imaging to exclude serious gastrointestinal pathology 2
• Do not order routine colonoscopy after CT-confirmed uncomplicated diverticulitis—only indicated for age-appropriate screening not yet performed, or if abscess/perforation/fistula present 2, 6
• Beware of pericolonic lymphadenopathy >1 cm on CT—this suggests malignancy rather than diverticulitis and requires colonoscopy 6, 7