Definition

Key History

Key Physical Exam

Risk Factors

• Chronic diseases: Inflammatory bowel, gout
• Enhanced enteric oxalate absorption (e.g., gastric bypass procedures, bariatric surgery, short bowel syndrome)
• Family history of stones
• Grapefruit juice consumption
• Marathon runners and those with decreased fluid intake
• Medications: HIV protease inhibitors (indinavir), diuretics

Differential Diagnosis

Diagnostic Testing

1. Urinalysis: Hematuria (may not be present - 15%), evaluate for crystals.
2. Urine culture if indicated by suspicion of infection.
3. Noncontrast computed tomography (NCCT) of the abdomen and pelvis is the gold standard for the initial evaluation of suspected kidney stones due to its high sensitivity and specificity. It can accurately determine the size, location and density of stones as well as identify complications such as hydronephrosis or alternative diagnoses. The American College of Radiology (ACR) recommends NCCT as the first-line imaging modality for patients with acute onset of flank pain and suspicion of stone disease. Ultrasonography (US) is another important diagnostic tool, particularly useful in specific populations such as pregnant women and children where radiation exposure from CT should be avoided. Although US has lower sensitivity and specificity compared to NCCT, it is effective in detecting hydronephrosis and larger stones.
4. Plain abdominal X-ray (KUB film) may be helpful in following the progress of an already-diagnosed, relatively large radiopaque stone. Not used frequently with availability of CT scanning, as it has low sensitivity and low specificity for identifying stones.
5. Calculus analysis of any stones or fragments collected. May help urologist or internist with treatment to decrease subsequent stone formation.

Treatment

Conservative Management:

• Pain Control: The first priority during an episode of renal colic is pain relief, typically achieved with nonsteroidal anti-inflammatory drugs (NSAIDs).
• Medical Expulsive Therapy (MET): For stones less than 10 mm, alpha-blockers such as tamsulosin can facilitate stone passage.
• Hydration and Dietary Modifications: Increased fluid intake to achieve a urine volume of at least 2.5 L/day is essential. Dietary modifications include reducing sodium, animal protein and oxalate intake while maintaining adequate dietary calcium.

Pharmacological Management:

• Thiazide Diuretics: For patients with recurrent calcium stones and hypercalciuria, thiazides are recommended.
• Potassium Citrate: Used for patients with hypocitraturia to prevent stone formation.
• Allopurinol: Indicated for calcium oxalate stone formers with hyperuricosuria.
• Specific Treatments: For uric acid stones, alkali therapy is the standard of care. Cystine stones may require thiol-binding agents like tiopronin if conservative measures fail.

Surgical Interventions:

• Extracorporeal Shock Wave Lithotripsy (ESWL): Suitable for most stones less than 2 cm in the kidney or upper ureter.
• Ureteroscopy: Utilizes laser energy to fragment stones and is effective for stones in the ureter or kidney.
• Percutaneous Nephrolithotomy (PCNL): Indicated for larger stones (>2 cm) or complex stone burdens, involving direct access to the kidney through the skin.

Follow-Up and Prevention:

• Monitoring: Follow-up imaging within 14 days to assess stone position and potential complications.
• Metabolic Evaluation: All patients should be screened for risk factors of stone recurrence, and those at high risk should undergo a detailed metabolic assessment.

Clinical Risk and Safety Pearls

• Patients on chemotherapy for malignancy are at increased risk for developing uric acid stones.
• Family history of stones may help suggest the diagnosis.
• Evaluation for the underlying cause of calculus formation may be performed as an outpatient; this may include consultation with a urologist and/or nephrologist and includes a stone analysis.
• If the patient has fever, consider stone complicated by infection, an indication for admission.
• A urinary tract infection with a kidney stone together requires IV antibiotics and admission.
• There is no evidence that forced diuresis enhances the passing of a stone, but high fluid intake by diluting the urine may ameliorate the prevalence of stone recurrence or enlargement.
• CT scan or ultrasound should be performed to determine the diagnosis. While scanning, it is useful to rule out abdominal aortic aneurysm and other acute causes of pain.
• Pain may actually radiate into the genitalia or present in an atypical fashion with isolated testicular pain.
• A passed stone can present without any identifiable stone on X-ray, but with hydroureter and hydronephrosis.

Complications

• May lead to persistent renal obstruction, decreased glomerular filtration rate.
• Over the years, Staghorn calculi can lead to renal failure if they are present bilaterally.