What is the diagnosis and recommended treatment for an adult patient presenting with abdominal pain, hematuria, impaired renal function, leukocyturia, and proteinuria?

Urinary Tract Infection with Possible Acute Interstitial Nephritis

This clinical presentation—abdominal pain, hematuria, leukocyturia, trace proteinuria, and low specific gravity—most likely represents a urinary tract infection (UTI), but the constellation of findings should prompt consideration of acute interstitial nephritis (AIN), particularly if there is recent NSAID or medication exposure. 1

Immediate Diagnostic Approach

Obtain a urine culture immediately, preferably before initiating antibiotics, to identify the causative organism and guide targeted therapy. 1 The presence of leukocytes strongly suggests infection, though leukocyturia alone does not exclude other pathology. 1

Critical Laboratory Evaluation

• Measure serum creatinine and BUN to assess renal function, as the low specific gravity (suggesting impaired concentrating ability) may indicate underlying renal impairment. 1
• Confirm microscopic hematuria with ≥3 RBCs per high-power field on microscopic examination, not just dipstick positivity, which has limited specificity (65-99%). 1, 2
• Examine urinary sediment for dysmorphic RBCs (>80% suggests glomerular disease) and white blood cell casts (suggests pyelonephritis or interstitial nephritis). 2, 3
• Quantify proteinuria using spot urine protein-to-creatinine ratio—trace protein on dipstick is typically <0.2 g/g, which argues against significant glomerular disease. 2

Medication History is Critical

Specifically inquire about recent NSAID use (ibuprofen, naproxen, diclofenac), as these commonly cause acute interstitial nephritis presenting with abdominal/flank pain, hematuria, leukocyturia, and impaired renal function within 1-4 days of exposure. 4 This diagnosis should be strongly considered if the patient has taken NSAIDs recently, even in the absence of fever or rash (which are present in only a minority of AIN cases). 4

Differential Diagnosis Priority

Most Likely: Urinary Tract Infection (UTI)

• Leukocyturia with hematuria and abdominal pain classically indicates UTI, particularly if accompanied by dysuria, urgency, or frequency. 1
• However, pyuria does not exclude other serious pathology—never delay complete evaluation based solely on presumed infection. 2
• If UTI is confirmed, treat with appropriate antibiotics based on culture results, but re-evaluate if symptoms persist beyond 48-72 hours of appropriate therapy. 1

High Priority Alternative: Acute Interstitial Nephritis

• Recent NSAID exposure (within 1-4 days) combined with flank/abdominal pain, hematuria, leukocyturia, and impaired concentrating ability (low specific gravity) strongly suggests AIN. 4
• AIN typically presents with normal urine output despite elevated creatinine, distinguishing it from prerenal azotemia. 4
• Renal biopsy may show mild interstitial inflammation or even appear normal in early disease, so clinical suspicion based on medication history is paramount. 4
• Treatment involves immediate discontinuation of the offending agent and supportive care with IV fluids; corticosteroids may be considered in severe cases. 4
• Renal function typically normalizes within 7-16 days after drug discontinuation. 4

Must Exclude: Urolithiasis

• The combination of abdominal pain and hematuria most commonly indicates urolithiasis, though the absence of colicky flank pain radiating to the groin makes this less likely. 3
• Ultrasound of kidneys and bladder is the appropriate initial imaging test for most patients with painful hematuria, with CT reserved for cases where ultrasound is negative but clinical suspicion remains high. 3
• A significant number of patients with urolithiasis do not have hematuria, so its presence is supportive but not required for diagnosis. 3

Imaging Strategy

Do not proceed with imaging until infection is excluded and renal function is assessed. 3 The low specific gravity and trace proteinuria suggest possible renal impairment, which would influence contrast decisions.

• If urine culture is negative and symptoms persist, obtain renal and bladder ultrasound to evaluate for stones, hydronephrosis, or structural abnormalities. 3
• CT urography without contrast may be obtained if ultrasound is negative but clinical suspicion for urolithiasis remains high, particularly if detection of a stone would impact treatment decisions. 3
• Trace/microscopic hematuria does not require emergency imaging in the absence of trauma, hemodynamic instability, or gross hematuria. 3

Treatment Approach

If UTI is Confirmed:

• Initiate empiric antibiotics after obtaining urine culture, adjusting based on susceptibility results. 1
• Ensure adequate hydration to maintain urine output and prevent further renal injury. 4
• Re-evaluate within 48-72 hours—if symptoms persist despite appropriate antibiotics, this effectively rules out simple UTI and mandates further investigation. 2

If AIN is Suspected:

• Immediately discontinue all NSAIDs and other potentially nephrotoxic medications. 4
• Provide aggressive IV hydration to support renal function. 4
• Monitor serum creatinine daily until improvement is documented. 4
• Consider nephrology referral if creatinine continues to rise or does not improve within 3-5 days of drug discontinuation. 2

Critical Red Flags Requiring Urgent Re-evaluation

• Gross hematuria develops—this carries a 30-40% malignancy risk and requires urgent urologic referral regardless of other findings. 2, 5
• Serum creatinine rises or fails to improve within 3-5 days of treatment. 2
• Development of significant proteinuria (protein-to-creatinine ratio >0.5 g/g), which would suggest glomerular disease requiring nephrology referral. 2
• Symptoms persist beyond 48-72 hours of appropriate antibiotic therapy, which effectively rules out simple UTI. 2

Common Pitfalls to Avoid

• Never assume leukocyturia alone confirms UTI—obtain culture confirmation before committing to prolonged antibiotic therapy. 1, 2
• Do not skip medication history, particularly regarding NSAIDs, which are available over-the-counter and patients may not consider them "real medications." 4
• Do not delay evaluation due to trace findings—even trace proteinuria and microscopic hematuria require systematic evaluation if persistent. 1, 2
• Never attribute hematuria solely to infection without confirming resolution after treatment—persistent hematuria after UTI treatment requires complete urologic evaluation. 2