Should a patient with hematuria, positive nitrite, and leukocytes in urinalysis undergo a CT scan to check for kidney stones?

Should This Patient Get a CT Scan?

No, this patient should NOT get a CT scan for kidney stones—they need treatment for a urinary tract infection (UTI) first. The presence of nitrites and leukocytes alongside hematuria indicates an active infection, which must be addressed before pursuing stone imaging 1.

Clinical Reasoning

Why This is a UTI, Not Stone Disease

The urinalysis findings point to infection as the primary diagnosis:

• Nitrites are highly specific for bacterial UTI (produced by gram-negative bacteria converting urinary nitrates) 1
• Leukocytes indicate pyuria (white blood cells responding to infection) 1
• Hematuria in this context is likely secondary to infection-induced mucosal inflammation, not necessarily stone disease 1

The Imaging Decision Algorithm

Step 1: Rule out infected obstructed kidney (urological emergency)

• Check for fever, elevated inflammatory markers (CRP), and flank pain 2
• If signs of obstruction with infection are present (fever + hydronephrosis), this requires immediate urological decompression before any other intervention 2

Step 2: Treat the infection first

• Initiate appropriate antibiotic therapy based on local resistance patterns
• Repeat urinalysis after treatment completion

Step 3: Reassess need for stone imaging

• If hematuria resolves after treating the UTI, no CT is needed 1

• If hematuria persists after infection clearance AND the patient has:

  • Flank pain suggestive of renal colic, OR
  • Risk factors for stones (family history, metabolic disease), OR
  • Recurrent UTIs suggesting anatomic abnormality

  Then consider imaging with ultrasound first (to limit radiation), followed by low-dose non-contrast CT if ultrasound is inconclusive 3, 4

When CT Would Be Appropriate

Non-contrast CT abdomen/pelvis is the gold standard for stone detection (97% sensitivity) but should only be ordered when 1, 3:

• Clinical suspicion for symptomatic stone disease (acute flank pain, renal colic) persists after infection treatment
• Ultrasound shows moderate-to-severe hydronephrosis (these patients have higher stone passage failure risk) 1
• Patient has recurrent symptoms despite negative initial workup 2

Low-dose CT protocols (<3 mSv) maintain excellent diagnostic accuracy (sensitivity 97%, specificity 95%) and should be used when CT is necessary 1, 3

Critical Pitfalls to Avoid

• Never assume hematuria automatically means stones—infection is a far more common cause when nitrites/leukocytes are present 1
• Don't order CT during active infection—inflammatory changes can mimic or obscure stone disease 1
• Absence of hydronephrosis on ultrasound does NOT rule out stones (NPV only 65%), but this is irrelevant until infection is cleared 1, 3
• Contrast-enhanced CT obscures stones in the collecting system—always use non-contrast protocol if stone imaging is needed 1

Special Considerations

If this patient has fever or appears septic, ultrasound should be performed urgently to rule out pyonephrosis (infected obstructed kidney), which requires emergency decompression regardless of stone presence 2. This is a true urological emergency with significant mortality risk if missed.