Is this presentation more likely a UTI or a kidney stone?

Clinical Presentation: Acute Pyelonephritis with Possible Concurrent Nephrolithiasis

This presentation is most consistent with acute pyelonephritis, though concurrent kidney stone disease cannot be excluded and must be actively investigated given the hematuria and flank pain. The combination of fever, flank pain, leukocyte esterase positivity, elevated WBC (17), and hematuria strongly suggests upper urinary tract infection, while the presence of significant hematuria raises concern for stone disease as either a primary or complicating factor 1.

Diagnostic Reasoning

Features Supporting Pyelonephritis

• Fever with flank pain is the hallmark presentation of acute pyelonephritis, typically occurring with temperatures >38°C and costovertebral angle tenderness 1
• Positive leukocyte esterase (+2) indicates pyuria, which is expected in pyelonephritis 1
• Elevated WBC of 17 represents systemic inflammatory response consistent with upper tract infection 1
• Dysuria and burning can occur with pyelonephritis, especially when concurrent lower tract symptoms are present 1

Features Suggesting Possible Stone Disease

• Significant hematuria (+3 blood) is more characteristic of nephrolithiasis than uncomplicated pyelonephritis 2, 3
• Flank pain occurs in both conditions but is classically colicky in stone disease versus constant/dull in pyelonephritis 2
• The negative nitrite finding is notable—while nitrites can be negative in early or low-bacterial-count infections, this reduces confidence in typical uropathogen presence 1
• Negative bacteria on urinalysis is unusual for pyelonephritis but can occur if the specimen was dilute or if urease-producing organisms are present (which may not show typical bacteriuria) 4

Critical Diagnostic Consideration: Infection Stones

The combination of UTI symptoms with hematuria and negative bacteria raises concern for infection stones (struvite calculi), which create a dangerous cycle of recurrent infection and stone growth 2, 4. These stones:

• Develop from urease-producing organisms (Proteus, Klebsiella, Pseudomonas) that create alkaline urine 2, 4
• Can harbor bacteria within the stone matrix, making them difficult to sterilize with antibiotics alone 2
• Require complete stone removal to eradicate infection 2
• May present with persistent or recurrent UTIs despite appropriate antibiotic therapy 3, 4

Immediate Management Algorithm

Step 1: Obtain Urine Culture Immediately

• Urine culture with antimicrobial susceptibility testing is mandatory in all suspected pyelonephritis cases before initiating antibiotics 1
• This is critical given the negative bacteria on urinalysis, which may indicate unusual organisms or low bacterial counts 1

Step 2: Imaging to Rule Out Obstruction and Stone Disease

Renal ultrasound should be performed urgently to evaluate for:

• Urinary tract obstruction (which can rapidly progress to urosepsis if present) 1, 5
• Kidney stones 1
• Renal abscess or other complications 1

The European Association of Urology guidelines specifically recommend upper urinary tract evaluation in patients with history of urolithiasis, which this patient's hematuria suggests 1. If ultrasound is inconclusive and symptoms persist after 72 hours of treatment, contrast-enhanced CT should be obtained 1.

Step 3: Initiate Empiric Antibiotic Therapy

Start empiric treatment for pyelonephritis immediately after obtaining urine culture 1, 6:

For outpatient management (if patient is not severely ill):

• Ciprofloxacin 500-750 mg PO twice daily for 7 days, OR 1, 6
• Levofloxacin 750 mg PO once daily for 5 days 1

For hospitalized patients or severe illness:

• Ciprofloxacin 400 mg IV twice daily, OR 1
• Ceftriaxone 1-2 g IV once daily 1

Step 4: Monitor Response and Adjust Based on Imaging

If fever persists beyond 72 hours of appropriate antibiotic therapy, this indicates possible complications requiring additional imaging 1:

• Obstructive pyelonephritis
• Renal abscess
• Infection stone 2

Common Pitfalls to Avoid

• Delaying imaging in patients with hematuria and suspected pyelonephritis—the combination mandates stone evaluation 1, 3
• Assuming negative bacteria on urinalysis rules out infection—urine culture is definitive and may reveal organisms not detected on urinalysis 1
• Failing to recognize that stones and infection often coexist, with each complicating the other 3, 5
• Not recognizing that infection stones require surgical removal, not just antibiotics, for cure 2
• Missing obstructive pyelonephritis, which requires urgent drainage to prevent permanent renal damage and sepsis 1, 5

Most Likely Diagnosis

This is most likely acute pyelonephritis (possibly with concurrent nephrolithiasis) based on the fever, flank pain, pyuria, and systemic inflammatory response 1. However, the significant hematuria and negative bacteria make concurrent stone disease highly probable, and approximately 15% of stone formers have infection as the cause of their stones 3. The patient requires both antimicrobial therapy and urgent imaging to definitively establish whether stones are present and contributing to the clinical picture 1, 3.