What are the differential diagnoses for a urinary tract infection (UTI)?

Differential Diagnoses for Urinary Tract Infection

When evaluating a patient with suspected UTI, the key differentials depend on whether symptoms suggest lower tract (cystitis) versus upper tract (pyelonephritis) involvement, and whether the presentation is uncomplicated or complicated. 1

Lower Tract Symptoms (Dysuria, Frequency, Urgency)

When a patient presents with dysuria, frequency, and urgency without fever or systemic symptoms, consider these differentials:

Genitourinary Conditions

• Vaginitis or vulvovaginitis - Look for vaginal discharge or irritation; dysuria with concomitant vaginal discharge significantly reduces UTI likelihood to <10% 2, 3
• Vulvar lesions - Examine for herpetic lesions, trauma, or other visible pathology 3
• Urethritis from sexually transmitted infections - Consider Chlamydia trachomatis or Neisseria gonorrhoeae, especially with new sexual partner or high-risk sexual behavior 3
• Atrophic vaginitis - Particularly in postmenopausal women; examine for vaginal atrophy 1

Non-Infectious Irritation

• Chemical or physical irritants - History of spermicide use, new soaps, bubble baths, or douches 1, 3
• Interstitial cystitis/bladder pain syndrome - Chronic symptoms without positive cultures, often with baseline genitourinary symptoms between episodes 1

Structural Abnormalities

• Bladder or urethral diverticula - May present with recurrent symptoms and incomplete emptying 1
• Pelvic organ prolapse (cystocele) - Examine for prolapse, particularly in postmenopausal women with recurrent symptoms 1

Upper Tract Symptoms (Fever, Flank Pain)

When systemic symptoms are present (fever, flank pain, costovertebral angle tenderness), consider:

Renal and Ureteral Pathology

• Nephrolithiasis (kidney stones) - CT imaging useful if symptoms persist beyond 72 hours or if stone suspected 1
• Renal abscess - Consider if no response to appropriate antibiotics within 48-72 hours; contrast CT is preferred imaging 1
• Perinephric abscess - Similar presentation to renal abscess with persistent fever despite treatment 1

Intra-Abdominal Pathology

• Diverticulitis - Particularly if history of prior diverticulitis; may present with pneumaturia or fecaluria 1
• Appendicitis - Right-sided flank pain may mimic pyelonephritis
• Pelvic inflammatory disease - In sexually active women with fever and pelvic pain 3

Other Infectious Causes

• Urosepsis - Systemic infection with hemodynamic instability; bacteremia occurs in 4-36% of neonatal/infant UTIs 1
• Prostatitis - In males with fever, dysuria, and pelvic/perineal pain 1, 4

Complicated UTI Risk Factors

The following conditions increase risk for complicated UTI and should prompt consideration of alternative or concurrent diagnoses: 1

• Anatomical abnormalities: Urinary tract obstruction, fistulae, indwelling catheters
• Functional abnormalities: Voiding dysfunction, neurogenic bladder, high post-void residuals
• Host factors: Pregnancy, diabetes mellitus, immunosuppression, renal transplant
• Prior history: Urinary tract surgery/trauma, abdominopelvic malignancy, recurrent pyelonephritis

Key Diagnostic Pitfalls

Asymptomatic Bacteriuria (ASB)

• Presence of positive urine culture without UTI symptoms - Do NOT treat in non-pregnant women, elderly patients, diabetics, or those with recurrent UTIs 1
• Pyuria alone is NOT diagnostic - Pyuria has exceedingly low positive predictive value and indicates genitourinary inflammation from many non-infectious causes 1

Catheter-Associated Considerations

• Urinalysis has very low specificity in patients with indwelling catheters or ileal conduits - Bacteriuria is almost always present regardless of symptoms 1
• Fever workup in hospitalized patients - Routine UA and cultures for fever lead to unnecessary testing; UTI/CAUTI rarely causes fever without urinary tract obstruction 1

Elderly Patients

• Genitourinary symptoms in elderly women are not necessarily UTI-related - Consider baseline incontinence, cognitive changes, or other age-related conditions 1

Clinical Decision Algorithm

For patients with acute-onset dysuria:

1. Assess for vaginal discharge/irritation - if present, consider vaginitis over UTI 2, 3
2. Check for fever/flank pain - if present, consider pyelonephritis or alternative upper tract pathology 2
3. Evaluate risk factors for complicated UTI - if present, broaden differential 1
4. If classic lower tract symptoms without vaginal symptoms in otherwise healthy woman, UTI diagnosis can be made clinically without culture 1

For patients with fever and suspected upper tract involvement:

1. Assess response to antibiotics at 48-72 hours - if no improvement, obtain imaging (CT preferred) to evaluate for abscess, stones, or obstruction 1
2. Consider alternative intra-abdominal pathology if presentation atypical 1