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. Blood tests:
   • CMP for serum electrolytes, blood urea nitrogen (BUN), creatinine, calcium, and phosphate levels and uric acid level
   • Controversial whether needed to routinely evaluate BUN and creatinine for signs of renal insufficiency
4. CT of the abdomen and pelvis without contrast performed using local radiation dose scanning technology is the preferred exam for most adults. This exam is available at most sites. If low radiation dose CT technology is not available, standard dose, noncontrast CT of the abdomen and pelvis or ultrasound of the kidneys and bladder are the two second-line alternatives.
5. Intravenous pyelogram - it is not sensitive to small stones, and the use of iodine-containing contrast media may induce an allergic or anaphylactic reaction. It may also cause deterioration of renal function in patients with pre-existing renal damage.
6. Renal ultrasonography is useful if patient with suspected stone disease is pregnant or is a child – decrease radiation exposure from CT scan. The color Doppler methods are the most accurate. Limited to evaluation in kidneys, renal pelvis, and proximal ureters
7. 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.
8. Calculus analysis of any stones or fragments collected. May help urologist or internist with treatment to decrease subsequent stone formation

Treatment

1. Medications for pain control (e.g. opiate and/or NSAIDs)
2. Obtain appropriate imaging to diagnose the presence of a stone and to rule out obstruction and hydronephrosis.
3. If there is urinary tract infection with a kidney stone then IV antibiotics and admission should be performed.
4. For smaller stones (e.g. <10mm), the use of medical therapies to promote stone passage may be of benefit. Agents used include alpha blockers (e.g. tamsulosin) and calcium channel blockers (e.g. nifedipine), sometimes in combination with a corticosteroid (e.g. prednisone).
5. Urologic referral should be considered for patients with:
   1. Fever or UTI and any evidence of obstruction
   2. Pregnancy
   3. Prior history of recurrent calculi
   4. History of renal failure or single kidney
   5. Pain refractory to medical management
   6. Inability to tolerate oral liquids due to refractory nausea and vomiting
6. Nephrology referral in presence of renal insufficiency (elevated serum creatinine and/or oliguria)
7. Spontaneous passage is highly dependent upon stone size (90% of stones <5mm pass spontaneously compared with 10% of stones >1cm)
8. Surgical interventions include extracorporeal shockwave lithotripsy, ureteroscopic extraction, percutaneous nephrolithotomy, and open pyelolithotomy.
9. Secondary prevention methods include adequate hydration practice, medications indicated as a result of a metabolic workup, and the use of dietary modifications such as a low-salt and/or protein diet.
10. Patients with single kidney and stones should be admitted or have close urologic follow up.

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.
• Decreased fluid intake and increased fluid losses (summer time, outdoor activity). Coffee (decaffeinated or regular) and wine drinkers have lower rates of stone formation.
• Evaluation for the underlying cause of calculus formation may be performed as an outpatient; this may include consultations 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 years, Staghorn calculi can lead to renal failure if they are present bilaterally.