What is the appropriate evaluation and treatment for a patient presenting with dysuria and left lower quadrant (LLQ) pain, suspected to have a urinary tract infection (UTI) or kidney stone?

Evaluation and Management of Dysuria with Left Lower Quadrant Pain

Order CT abdomen and pelvis with IV contrast immediately as the single most important diagnostic test, as this presentation requires urgent evaluation to distinguish between urinary tract infection, kidney stone, and potentially life-threatening conditions like diverticulitis or abscess. 1, 2

Initial Diagnostic Approach

Obtain urinalysis and urine culture immediately to identify urinary tract infection, which is the most common cause of dysuria, while simultaneously ordering imaging to evaluate the left lower quadrant pain. 3, 4 The combination of dysuria with LLQ pain expands the differential beyond simple cystitis to include:

• Pyelonephritis with left kidney involvement - look for fever, flank pain, and costovertebral angle tenderness 1, 3
• Obstructive pyelonephritis from kidney stone - a urologic emergency that can progress to sepsis and death 5
• Diverticulitis - the most common cause of LLQ pain in adults, affecting 10-25% of patients with diverticulosis 1, 2
• Infected kidney stone - urease-producing bacteria can cause struvite stones with accompanying infection 5, 6

Why CT with IV Contrast is Essential

CT abdomen and pelvis with IV contrast has 98% diagnostic accuracy and is rated 8/9 (usually appropriate) by the American College of Radiology. 1, 2 This single test will:

• Detect kidney stones with near 100% sensitivity (though unenhanced CT is actually preferred for stone detection) 1
• Identify complications requiring urgent intervention: abscess, perforation, obstruction 1, 2
• Distinguish diverticulitis from perforated colon cancer (look for pericolonic lymphadenopathy >1 cm) 1, 2
• Detect hydronephrosis indicating obstructive uropathy 1
• Identify alternative diagnoses in up to 49% of cases 2

Critical caveat: If kidney stone is the primary clinical suspicion based on acute onset severe colicky pain with hematuria, unenhanced CT is actually superior as IV contrast can obscure small stones. 1 However, given the LLQ pain component, contrast-enhanced CT provides more comprehensive evaluation of both urinary and gastrointestinal pathology.

Red Flags Requiring Emergency Evaluation

Immediately escalate care if any of these are present:

• Fever with inability to pass gas or stool - suggests complicated diverticulitis or obstruction 2, 7
• Severe abdominal tenderness with guarding or rebound - indicates peritonitis requiring surgical consultation 2, 7
• Signs of septic shock (hypotension, tachycardia, altered mental status) - requires emergent broad-spectrum antibiotics and possible surgery 2
• Vomiting with progressively worsening pain - suggests obstruction or complicated infection 2

Laboratory Evaluation

Order these tests immediately:

• Urinalysis with microscopy - pyuria and bacteriuria confirm UTI; hematuria suggests stone or malignancy 3, 4
• Urine culture - essential for guiding antibiotic therapy, especially in complicated or recurrent infections 3, 4
• Complete blood count - leukocytosis >15,000 with left shift suggests bacterial infection 2
• C-reactive protein - CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity 2
• Serum creatinine - assess renal function, especially if obstruction suspected 1

Management Algorithm Based on Findings

If Urinalysis Shows Infection WITHOUT Imaging Abnormalities:

Treat as uncomplicated UTI only if:

• No fever or systemic symptoms
• Pain is suprapubic, not LLQ
• No history of kidney stones or diverticulosis
• Patient can tolerate oral intake

Use trimethoprim-sulfamethoxazole for 3 days (for uncomplicated cystitis in women) or 7-14 days (for complicated UTI or pyelonephritis). 8, 3

If CT Shows Kidney Stone:

Stones <5 mm: Conservative management with hydration, pain control, and spontaneous passage expected 9

Stones >5 mm with hydronephrosis: Urology consultation for possible intervention (lithotripsy or ureteroscopy) 5, 9

Obstructive pyelonephritis (stone + infection + fever): This is a urologic emergency requiring:

• Immediate broad-spectrum IV antibiotics
• Emergent decompression (ureteral stent or percutaneous nephrostomy)
• Urology consultation within hours, not days 5

If CT Shows Diverticulitis:

Uncomplicated diverticulitis (wall thickening, fat stranding, no abscess):

• Conservative management WITHOUT antibiotics is appropriate for immunocompetent patients 2
• Clear liquid diet advancement as tolerated
• Oral analgesics for pain control
• Antibiotics only for immunocompromised or elderly patients: Ertapenem 1g q24h or Eravacycline 1mg/kg q12h for maximum 7 days 2

Complicated diverticulitis with small abscess (<4 cm):

• Antibiotics alone for 7 days without drainage 2

Complicated diverticulitis with large abscess (≥4 cm):

• Percutaneous drainage PLUS antibiotics for 4 days 2

Perforation with free air or diffuse peritonitis:

• Emergency surgical consultation
• NPO, IV fluids, nasogastric decompression
• Broad-spectrum IV antibiotics immediately 2

Special Considerations for Women of Childbearing Age

If premenopausal woman with possible gynecologic pathology:

• Obtain pregnancy test first
• Consider pelvic/transvaginal ultrasound as initial imaging instead of CT 1
• Vaginal discharge decreases likelihood of UTI and suggests cervicitis - obtain vaginal cultures 3

Common Pitfalls to Avoid

Do not treat empirically without imaging when LLQ pain is present - clinical diagnosis alone has 34-68% misdiagnosis rate for diverticulitis. 1, 2

Do not miss colon cancer - pericolonic lymphadenopathy >1 cm on CT strongly suggests malignancy rather than diverticulitis and mandates colonoscopy. 1, 2, 7

Do not delay imaging in obstructive pyelonephritis - this can progress to sepsis within hours. Fever + flank pain + pyuria = emergent imaging. 5

Do not continue antibiotics beyond 7 days for uncomplicated diverticulitis - this increases resistance without improving outcomes. 2

Follow-up and Recurrence Prevention

For kidney stones: Increase fluid intake to produce 2-2.5L urine daily, dietary modifications based on stone composition, consider citrate supplementation. 9

For diverticulitis: Colonoscopy is NOT routinely needed after CT-confirmed uncomplicated diverticulitis, except for age-appropriate screening or if abscess/perforation/fistula present. 1, 2

For recurrent UTI: Repeat urine culture to guide therapy, consider imaging to exclude anatomic abnormalities or stones. 3, 4