What is the likely cause of persistent fever, hematuria, and non-specific mild right pelvocaliectasia in a patient with no dysuria or genital itching?

Differential Diagnosis for Persistent Fever with Hematuria and Right Pelvocaliectasis

The most likely diagnosis is acute pyelonephritis of the right kidney, given the combination of persistent fever, hematuria, and mild right pelvocaliectasis, even in the absence of classic lower urinary tract symptoms. 1

Primary Differential Considerations

1. Acute Pyelonephritis (Most Likely)

• Fever with hematuria and unilateral pelvocaliectasis strongly suggests upper urinary tract infection. 1
• Up to 20% of pyelonephritis patients lack bladder symptoms (dysuria, urgency, frequency), making the absence of dysuria consistent with this diagnosis 1, 2
• Flank pain or costovertebral angle tenderness is nearly universal in pyelonephritis, though you should specifically assess for this finding 1, 3
• The mild pelvocaliectasis likely represents inflammatory changes from acute infection rather than chronic obstruction 1

Key diagnostic steps:

• Obtain urinalysis looking specifically for pyuria (≥10 WBCs/high-power field) and bacteriuria 4
• If pyuria is present, proceed with urine culture with antimicrobial susceptibility testing 4, 1
• Obtain complete blood count with differential to assess for leukocytosis (>14,000 cells/mm³) or left shift (>6% bands or >1500 bands/mm³), which have high likelihood ratios (14.5,7.5, and 4.7 respectively) for bacterial infection 4
• Consider blood cultures if urosepsis is suspected (high fever, chills, hypotension) 4

2. Vesicoureteral Reflux with Secondary Infection

• The ultrasound report specifically mentions this as a possibility 1
• This would explain the pelvocaliectasis and predispose to ascending infection
• More common in pediatric populations but can persist into adulthood
• Would still present as pyelonephritis clinically 1

3. Partial Urinary Obstruction with Secondary Infection

• Mild pelvocaliectasis suggests possible intermittent or partial obstruction
• Could be from stone disease, though typically presents with colicky flank pain
• Imaging within 48-72 hours is indicated if fever persists despite appropriate antibiotic therapy 1
• Consider CT urography if no improvement occurs 1

4. Renal Abscess or Complicated Pyelonephritis

• If fever persists beyond 72 hours of appropriate antibiotic therapy, imaging (CT with contrast) is mandatory to evaluate for abscess formation 1
• Microabscesses can coalesce into larger renal abscesses 1
• More likely in diabetic or immunocompromised patients 1

5. Non-Infectious Causes (Less Likely Given Fever)

• Acute interstitial nephritis (typically drug-induced)
• Glomerulonephritis (though typically presents with proteinuria and RBC casts)
• Renal infarction (would present with acute severe flank pain)

Critical Pitfalls to Avoid

Do not assume asymptomatic bacteriuria: The presence of fever with hematuria indicates symptomatic infection requiring treatment, not colonization 4

Do not delay urine culture: While urinalysis can guide initial management, culture with susceptibility testing is essential for pyelonephritis to ensure appropriate targeted therapy 1, 2

Do not overlook atypical presentations: The absence of dysuria does not exclude UTI, particularly upper tract infection 1, 2

Do not order unnecessary imaging initially: Imaging is not indicated for uncomplicated pyelonephritis at presentation but becomes essential if fever persists beyond 72 hours of appropriate therapy 1

Immediate Management Algorithm

1. Obtain urinalysis with microscopy immediately - if pyuria present, send urine culture 4
2. Check CBC with differential - assess for leukocytosis or left shift 4
3. Assess for systemic toxicity - if present (hypotension, altered mental status), obtain blood cultures and consider hospitalization 4
4. Initiate empiric antibiotic therapy for presumed pyelonephritis while awaiting culture results 1, 2
5. Reassess at 48-72 hours - if persistent fever, proceed with contrast-enhanced CT imaging 1
6. Consider high-risk factors - diabetes, immunosuppression, anatomic abnormalities warrant lower threshold for imaging and hospitalization 1