How is pain secondary to nephrolithiasis diagnosed and managed?

Diagnosis of Pain Secondary to Nephrolithiasis

The diagnosis of pain from kidney stones is established through clinical presentation of colicky flank pain combined with confirmatory imaging—ultrasound as the primary tool, with non-contrast CT as the gold standard when US is inconclusive or emergency intervention is being considered. 1

Clinical Presentation and History

The pain of nephrolithiasis has characteristic features that distinguish it from other causes of flank pain:

• Colicky nature: Pain occurs in waves of severe intensity followed by periods of less intense discomfort, caused by internal obstruction and distension of the collecting system rather than external compression 2
• Pain that worsens significantly with external flank pressure suggests alternative diagnoses such as pyelonephritis, kidney infection, or perinephric abscess rather than uncomplicated nephrolithiasis 2
• Obtain detailed history including prior stone episodes, family history of stones, and metabolic conditions, as these increase likelihood of recurrent disease 1

Initial Diagnostic Workup

Immediate Laboratory Testing

Every patient presenting with suspected nephrolithiasis requires:

• Urine dipstick to assess for hematuria (though absence does not exclude stones, as some pediatric and adult patients with confirmed stones lack hematuria) 1
• Blood tests: serum creatinine, uric acid, ionized calcium, sodium, potassium, complete blood count, and C-reactive protein 1
• Urine culture before any intervention, particularly if infection is suspected 3

Imaging Algorithm

Ultrasound is the primary diagnostic tool and should not delay emergency care 1:

• US has 45% sensitivity for detecting stones overall, with 94% specificity for ureteral stones and 88% for renal stones 1
• US is particularly valuable as first-line imaging in pregnant women and children 1
• Color Doppler with twinkling artifact assessment can improve sensitivity for small renal stones 2

Non-contrast CT is the gold standard when:

• US is inconclusive or negative but clinical suspicion remains high 1
• Acute flank pain requires definitive diagnosis 1
• CT provides sensitivity of 93-97% and specificity of 96.6% 1, 2
• CT also assesses stone location, burden, density, composition, and anatomic factors critical for treatment planning 1

Low-dose CT protocols should be used to minimize radiation exposure while maintaining diagnostic accuracy (93.1% sensitivity, 96.6% specificity) 1

KUB radiography (44-77% sensitivity) serves as an adjunct to differentiate radioopaque from radiolucent stones and aids in follow-up monitoring 1

Assessment for Urgent Complications

Before definitive treatment, evaluate for conditions requiring immediate intervention 3:

• Signs of infection: fever, elevated CRP, elevated white blood cell count 3
• Renal function compromise: check for anuria or bilateral obstruction 3
• If sepsis and/or anuria are present, urgent decompression via percutaneous nephrostomy or ureteral stenting is mandatory before definitive stone treatment 3

Stone Analysis and Risk Stratification

• Stone compositional analysis should be performed for all first-time stone formers to guide prevention strategies 1, 3
• More extensive metabolic evaluation (24-hour urine collection for lithogenic and litholytic substances) is reserved for high-risk patients: those with recurrent stones (≥2 episodes), bilateral disease, strong family history, or age ≤25 years 1, 4
• Consider genetic testing with next-generation sequencing for children, adults aged ≤25 years, or those with suspected inherited metabolic disorders 1

Common Pitfalls to Avoid

• Do not rely solely on hematuria presence: some confirmed stone patients lack hematuria on urinalysis 1
• Do not use CT as first-line in pregnant women or children: ultrasound is strongly recommended first, with MRI as second-line in pregnancy and low-dose CT only as last resort 1
• Do not delay imaging in emergency presentations: ultrasound should be performed immediately but should not delay emergency care for unstable patients 1
• Do not assume pain controlled with NSAIDs means no intervention needed: stones >10 mm rarely pass spontaneously and require surgical planning regardless of pain control 3, 5