Nephrolithiasis - Kidney Stone

Diagnosis

Indications for Testing

• Hematuria
• Flank pain
• Colicky back pain

Laboratory Testing

• Initial testing
  • Urinalysis
    • Point-of-care testing for hematuria
    • Urine microscopic testing
      • Blood indicates injury due to crystal passage
      • Crystals indicate the possibility of a stone
  • Urine culture – consider to evaluate for concomitant urinary tract infection
  • CBC – especially if symptoms of concomitant infection are present
  • Serum electrolytes – evaluate for electrolyte abnormalities
  • Blood urea nitrogen (BUN)/creatinine – evaluate for obstructive renal pathology
• 24-hour urine evaluation – use panel testing for most patients
  • Not usually performed with first stone, except in children (refer to Pediatrics)
  • Usually includes electrolyte analysis (eg, sodium) and metabolic analysis (eg, oxalate and calcium)
  • Collection of two different urine specimens is recommended

• Serum – uric acid, ionized calcium, and parathyroid hormone (PTH)-related peptide (PTHrP)
  • PTH testing may be reserved for recurrent disease unless primary hypoparathyroidism is a concern
• Amino acids analysis – evaluate when cystinuria is a concern or in those with cystine stones
• Stone collection and analysis
  • Repeat if there is lack of response to therapy, since stone composition may change

Differential Diagnosis

• Urinary tract infection
• Ectopic pregnancy
• Musculoskeletal pain
• Ovarian cyst rupture
• Ovarian torsion
• Peritonitis
• Prostatitis
• Acute pyelonephritis
• Interstitial cystitis
• Groin hernia

Screening

There is no evidence to support screening for stones in asymptomatic patients.

Monitoring

• Usually unnecessary in patients experiencing first stone
• If performed, usually includes a minimum of the following
  • Assessment within 6 months after treatment begins or changes; annually thereafter, depending on stone activity (American Urological Association, 2014)
  • 24-hour urine – kidney stone panel testing
    • 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

Background

Epidemiology

• Prevalence – 1-5/1,000
  • 1/11 affected during lifetime (Pearle, 2014)
• Sex – M>F, 1.3:1
• Ethnicity – White men have highest incidence
• Geography – greater incidence in hotter and drier climates

Risk Factors

Clinical Presentation

• Acute, colicky flank pain radiating into the pelvis and genitalia
• Hematuria – present in 90% of patients
• Nausea and vomiting
• Urinary urgency, frequency, and dysuria with stone passage

Pediatrics

Epidemiology

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

Clinical Presentation

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

Indications for Testing

Refer to Diagnosis

Laboratory Testing

• Refer to Diagnosis
• Differences in pediatric testing
  • 24-hour urine evaluation recommended in the first episode due to high risk of metabolic problems underlying stone formation
  • Amino acid analysis recommended
    • Evaluate for cystinuria in patients with elevated urine cystine – more common in children with nephrolithiasis

Monitoring

• More important in children, even in those with first stone
  • >75% of stones in children are secondary to metabolic problems
• Usually includes the following
  • Assessment within 6 months after treatment begins or changes
  • 24-hour urine evaluation – kidney stone panel testing
    • 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, ionized calcium