Indications for Testing

• Patient with symptoms of a stone

Laboratory Testing

• Initial testing
  • CBC – rule out concomitant infection
  • Electrolytes – rule out electrolyte abnormalities associated with vomiting
  • BUN/creatinine – rule out obstructive pathology
• Urine – kidney stone risk assessment on 24-hour urine (may delay this risk assessment until recurrent stone disease occurs); initial testing should include 2 different specimens
  • Amino acids analysis – rule out cystinuria
• Serum – uric acid, ionized calcium and parathyroid hormone-related peptide (PTH)
  • PTH may be reserved for recurrent disease
• Stone – calculi analysis

Imaging Studies

• Helical CT scan can confirm presence and location of stones

Differential Diagnosis

• Peritonitis
• Pyelonephritis
• Ovarian torsion
• Ovarian cyst
• Ectopic pregnancy
• Prostatitis
• Musculoskeletal pain

• No evidence to support screening for stones in asymptomatic patients

• Unnecessary in first-time stone former
• Usually includes:
  • Assessment 4-8 weeks after treatment
  • Urine – kidney stone risk assessment
    • Should include testing for calcium oxalate sodium, uric acid, citric acid, phosphorus, creatinine
    • Quantitative cystine in patients with cystinuria
  • Serum – urea nitrogen, creatinine and ionized calcium

Nephrolithiasis is a worldwide problem that accounts for significant morbidity and expense.

Epidemiology

• Prevalence – 1-5/1,000
• Age – peaks in 20s
• Sex – M>F, 2-3:1
• Ethnicity – Caucasian men have highest incidence
• Geographic – hotter and drier climates

Pathophysiology

• Calcium oxalate/calcium phosphate stones are the most common (70-90%)
  • Risk factors include dehydration, thiazide diuretics, increased intestinal absorption, excessive oxalate consumption, pregnancy, primary hyperparathyroidism, chronic bowel malabsorption and chronic use of calcium-containing products
• Magnesium ammonium phosphate stones (10-15%)
  • Risk factors include frequent urinary tract infections and presence of alkaline urine
  • Also referred to as struvite stones (staghorn calculi)
• Uric acid stones (5-15%)
  • Risk factors include gout, family history, malignancy treated with chemotherapy, and high purine diet
• Cystine stones (1-2%)
  • Risk factor is hereditary cystinuria

Clinical Presentation

• Acute, colicky flank pain radiating into the pelvis and genitals associated with nausea and vomiting
• Urinary urgency, frequency and dysuria may develop with stone passage
• Hematuria is present in 90% of patients

Prevention

• All stones – maintain urine volume ≥2 L/24-hours
• Uric acid stones – limit protein intake
• Cystine stones – limit protein and salt intake
• Calcium stones
  • Citrate supplementation if urine citrate is low
  • Restrict high oxalate foods
  • Restrict salt and protein intake

Clinical Background

Epidemiology

• Incidence – 4.7/100,000 hospitalized
• Lower than in adults

Clinical Presentation

• Flank pain, abdominal pain
  • <5 years – nonspecific; nausea, emesis
• Blood in urine, dysuria, urgency

Diagnosis

Indications for Testing

• Patient with symptoms of a stone

Laboratory Testing

• Initial testing
  • CBC – rule out concomitant infection
  • Electrolytes – rule out electrolyte abnormalities associated with vomiting
  • BUN/creatinine – rule out obstructive pathology
• Urine – kidney stone risk assessment on 24-hour urine (may delay this risk assessment until recurrent stone disease occurs); initial testing should include 2 different specimens
  • Amino acids analysis – rule out cystinuria
  • Urine amino acids analysis and culture – rule out cystinuria

Monitoring

• More important in children, even with first-time stone former
  • >75% of stones in children are secondary to metabolic problems
• Usually includes the following
  • Assessment 4-8 weeks after treatment
  • Urine – kidney stone risk assessment
    • Should include testing for calcium oxalate sodium, uric acid, citric acid, phosphorus, creatinine
    • Quantitative urine cystine or urine amino acids analysis in patients with cystinuria
  • Serum – urea nitrogen, creatinine and ionized calcium

Tests generally appear in the order most useful for common clinical situations

General

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