Nephrolithiasis - Kidney Stone

Diagnostic Algorithm

  Nephrolithiasis Testing Algorithm

Clinical Background

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

Diagnosis

Indications for Testing

• Patient with symptoms of a stone

Laboratory Testing

• Initial testing
  • Urine – urinalysis for hematuria, bacteria
  • 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 (this risk assessment may be delayed 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

Screening

Monitoring

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Click the plus sign to expand the table of additional tests.

Test Name and Number	Comments
Kidney Stone Risk Panel, Urine 0020843 Method: Refer to individual components	Preferred test is urine supersaturation profile
Kidney Stone Risk Panel II, Urine 0020805 Method: Refer to individual components	Tests for calcium, chloride, citric acid, cystine, magnesium, oxalate, phosphorous, potassium, sodium
Creatinine, Serum or Plasma 0020025 Method: Spectrophotometry
Creatinine, 24-Hour Urine 0020473 Method: Spectrophotometry
Oxalate, Urine 0020482 Method: Spectrophotometry
Citric Acid, Urine 0020852 Method: Enzymatic
Urea Nitrogen, Serum or Plasma 0020023 Method: Spectrophotometry
Uric Acid, Serum or Plasma 0020026 Method: Spectrophotometry
Calcium, Ionized, Serum 0020135 Method: Ion-Selective Electrode/pH-Electrode
Parathyroid Hormone-Related Peptide (PTHrP) 0093014 Method: Immunoradiometric Assay