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
  • Urine metabolic studies at ARUP

    Urine Metabolic Studies at ARUP

    Component	Kidney Stone Risk Panel, 0020843 (Basic Urine Panel)	Calculi Risk Assessment, 2008708 (Extended Urine Panel)	Supersaturation Profile, 2008771 Extended Urine Panel with Supersaturation Tests)
    Total volume	X	X	X
    pH		X	X
    Calcium	X	X	X
    Creatinine	X	X	X
    Oxalate	X	X	X
    Uric acid	X	X	X
    Chloride		X	X
    Citric acid	X	X	X
    Magnesium		X	X
    Phosphorus		X	X
    Potassium		X	X
    Sodium		X	X
    Sulfate			X
    Calcium oxalate supersaturation			X
    Calcium phosphate supersaturation			X
    Uric acid supersaturation			X

• 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 – Caucasian 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