How do you diagnose back pain caused by a renal stone (kidney stone)?

Diagnosing Back Pain from Renal Stones

Non-contrast CT of the abdomen and pelvis is the definitive test to diagnose back pain caused by kidney stones, with 97% sensitivity and 95% specificity, and should be performed using low-dose protocols to minimize radiation exposure. 1

Clinical Presentation That Suggests Renal Stone

The following features distinguish renal stone pain from other causes of back pain:

• Severe, colicky flank pain that radiates from loin to groin, often accompanied by nausea and vomiting 1, 2
• Hematuria (blood in urine) due to ureteral trauma from the stone 1, 2
• Urinary symptoms including dysuria, frequency, and oliguria 2
• Pain that does NOT worsen with external flank pressure or prolonged static positioning—if it does, consider musculoskeletal causes instead 3
• History of previous kidney stones makes recurrence highly likely, as approximately 50% of patients develop recurrent stones 2

Imaging Algorithm for Diagnosis

First-Line: Low-Dose Non-Contrast CT

Low-dose non-contrast CT (<3 mSv) is the gold standard and should be ordered first for any patient with suspected renal stones, providing:

• 97% sensitivity and 95% specificity for stone detection 1
• Precise stone localization, size measurement, and density assessment—all critical for management decisions 3
• Detection of secondary signs including hydronephrosis, periureteral inflammation, and perinephric edema 1
• Identification of alternative diagnoses in approximately one-third of patients with flank pain 3

Alternative Imaging: Ultrasound Plus Radiography

If CT is contraindicated (pregnancy, radiation concerns in young patients):

• Ultrasound combined with plain radiography (KUB) achieves 79-90% sensitivity for clinically significant stones 1, 4
• Ultrasound alone has only 24-57% sensitivity for stone detection but 100% sensitivity for hydronephrosis 4
• Color Doppler with twinkling artifact can improve sensitivity to 99% for stones <5 mm, though false-positive rates reach 60% 3
• Absence of hydronephrosis on ultrasound makes stones >5 mm less likely 3

Imaging to Avoid

• Plain radiography (KUB) alone has inadequate sensitivity (29% overall, 72% for large stones) and should never be used as the sole diagnostic test 3, 4
• Contrast-enhanced CT obscures small stones in the contrast-filled collecting system and is not appropriate for initial stone evaluation 1
• MRI has limited utility for stone detection and should only be considered when radiation must be avoided and ultrasound is inconclusive 4

Critical Red Flags Requiring Urgent Evaluation

Watch for these features that indicate complications requiring immediate intervention:

• Fever, chills, or systemic infection signs suggest obstructive pyelonephritis requiring emergent decompression 3
• Inability to urinate or decreased urine output indicates possible complete obstruction 3
• Visible hematuria with systemic symptoms warrants immediate assessment 3

Stone Characteristics That Guide Management

Once a stone is confirmed on imaging:

• Stones <5 mm typically pass spontaneously without intervention 3, 2
• Larger and more proximally located stones have lower spontaneous passage rates and higher need for intervention 1
• Stone size and location are the most important determinants for predicting spontaneous passage versus need for urologic procedures 1

Alternative Diagnoses to Consider

CT identifies non-stone causes in approximately one-third of patients with flank pain 3:

• Gastrointestinal causes: Right colonic diverticulitis, gastroenteritis, inflammatory bowel disease 3
• Gynecologic causes in women: Benign adnexal masses, pelvic congestion syndrome 3
• Musculoskeletal causes: Paraspinal muscle strain, facet joint pathology, lumbar spine disease—suspect these if pain worsens with external pressure or after prolonged positioning 3

Common Diagnostic Pitfalls

• Performing ultrasound too early (<2 hours from symptom onset) may miss secondary signs of obstruction that take time to develop 3
• Relying on clinical presentation alone without imaging, as back pain is nonspecific and associated with numerous other conditions 1
• Using only plain radiography in patients with recurrent stones, missing radiolucent stones and alternative diagnoses 3
• Ordering standard-dose CT instead of low-dose protocols, unnecessarily exposing patients to higher radiation 1, 4