Nephrolithiasis - Kidney Stone

Diagnosis

Indications for Testing

  • Patient with symptoms of a stone

Laboratory Testing

  • Initial testing
    • CBC – evaluate for concomitant infection
    • Electrolytes – evaluate for electrolyte abnormalities
    • Blood urea nitrogen (BUN)/creatinine – evaluate for obstructive renal pathology
    • Urinalysis with possible urine culture – evaluate for concomitant urinary tract infection
  • 24-hour urine evaluation – use panel testing for most patients
    • Not usually performed with first stone
      • Usually includes electrolyte analysis (eg, sodium) and metabolic analysis (eg, oxalate and calcium)
    • May delay risk assessment until stone disease recurs
    • Should include 2 different specimens
  • Amino acids analysis – evaluate for cystinuria in patients when cystinuria is suspected or for those with cystine stones
  • Serum – uric acid, ionized calcium, and parathyroid hormone-related peptide (PTH)
    • PTH testing may be reserved for recurrent disease unless primary hypoparathyroidism is suspected
  • Stone analysis
    • Repeat if lack of response to therapy since stone composition may change

Imaging Studies

  • Helical CT scan can confirm presence and location of stones
    • May help assess stone burden and risk of recurrence

Differential Diagnosis

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

Screening

  • No evidence to support screening for stones in asymptomatic patients

Monitoring

  • Unnecessary in first-time stone former
  • Usually includes the following
    • Assessment within 6 months after treatment begins or changes and thereafter annually, 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

Clinical Background

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

Epidemiology

  • Prevalence – 1-5/1,000
    • 1/11 affected during lifetime (Pearle, 2014)
  • Age – peaks in 20s
  • Sex – M>F, 2-3:1
  • Ethnicity – Caucasian men have highest incidence
  • Geographic – hotter and drier climates

Risk Factors

  • Risk factors for kidney stones

    Risk Factors for Kidney Stones

    Type of Stone

    Percentage of Stones

    Risk Factors

    Calcium oxalate/calcium phosphateMost common (70-90%)
    • Dehydration
    • Thiazide diuretics
    • Increased intestinal absorption
    • Pregnancy
    • Primary hyperparathyroidism 
    • Chronic bowel malabsorption 
    • Chronic use of calcium-containing products
    • Excessive consumption of
      • Oxalate
      • Phosphoric acid (cola products)
      • Sugar-sweetened beverages

    Magnesium ammonium phosphate

    Also referred to as struvite stones (staghorn calculi)

    10-15%
    • Frequent urinary tract infections
    • Presence of alkaline urine
    Uric acid5-15%
    • Gout
    • Family history of gout or stones
    • Malignancy treated with chemotherapy
    • Diet high in purines
    Cystine1-2%Hereditary cystinuria

Clinical Presentation

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

Prevention

  • All stones – maintain urine volume ≥2.5 L/day
  • Uric acid stones – limit intake of nondairy protein, allopurinol ( Agency for Healthcare Research and Quality [AHRQ], 2013 )
  • Cystine stones – limit intake of protein and salt
  • Calcium oxalate stones (AHRQ, 2013; American Urological Association, 2014 )
    • Increase intake of fluid
    • Reduce consumption of soft drinks
    • Thiazide diuretics
    • Citrate pharmacotherapy if urinary citrate is low
    • Reduce sodium and animal protein
    • If oxalate is relatively high – limit oxalate and use dairy products at mealtime to enhance binding of oxalate and calcium in gastrointestinal tract

Pediatrics

Clinical Background

Epidemiology

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

Clinical Presentation

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

Diagnosis

Indications for Testing

  • Patient with symptoms of a stone

Laboratory Testing

  • Initial testing
    • CBC – evaluate for concomitant infection
    • Electrolytes – evaluate for electrolyte abnormalities
    • Blood urea nitrogen (BUN)/creatinine – evaluate for obstructive renal pathology
    • Urinalysis with possible urine culture – evaluate for concomitant urinary tract infection
  • 24-hour urine evaluation
    • May delay this risk assessment until stone disease recurs
    • Initial testing should include 2 different specimens
  • Amino acids analysis
    • Evaluate for cystinuria – more common in children with nephrolithiasis

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 within 6 months after treatment begins or changes
    • 24-hour urine evaluation – kidney stone panels to assess
      • 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

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
Test Name and Number Recommended Use Limitations Follow Up
Calculi Risk Assessment, Urine 2008708
Method: Quantitative Spectrophotometry/Quantitative Enzymatic/Quantitative Ion-Selective Electrode

Acceptable initial urine test for kidney stone risk assessment and monitoring

Panel includes calcium, chloride, citric acid, creatinine, magnesium, oxalate, pH, phosphorus, potassium, sodium, and uric acid

   
Supersaturation Profile, Urine 2008771
Method: Quantitative Spectrophotometry/Quantitative Enzymatic/Quantitative Ion-Selective Electrode

Acceptable initial urine test for kidney stone risk assessment and monitoring; includes interpretation of data

Panel includes calcium, magnesium, sodium, sulfate, citric acid, oxalate, uric acid, potassium, creatinine (24-hour) chloride, and phosphorous

Assessment for risk of magnesium ammonium phosphate (struvite) calculi is not included in this profile

Does not test for urine cystine

If magnesium ammonium phosphate calculi are suspected, order plasma ammonia testing

If cystine calculi are suspected, order cystinuria panel, cystine quantitative urine or amino acids quantitative urine tests

Kidney Stone Risk Panel, Urine 0020843
Method: Quantitative Spectrophotometry/Quantitative Enzymatic

Preferred test is urine supersaturation profile or urinary calculi risk assessment, depending on calculation need

Panel includes calcium, citric acid, creatinine, oxalate, and uric acid

May be used to monitor kidney stone formation

   
Cystinuria Panel 0081105
Method: Quantitative Liquid Chromatography/Tandem Mass Spectrometry

Evaluate for cystinuria

Panel includes arginine, cystine, lysine, and ornithine

   
Cystine Quantitative, Urine 0081106
Method: Liquid Chromatography/Tandem Mass Spectrometry
Monitor treatment in patients with cystinuria
   
Amino Acids Quantitative by LC-MS/MS, Urine 2009419
Method: Quantitative Liquid Chromatography/Tandem Mass Spectrometry

Use for risk assessment if cystine stone is found

   
Calculi (Stone) Analysis 0099460
Method: Quantitative Reflectance Fourier Transform Infrared Spectroscopy/Quantitative Polarizing Microscopy

Determine composition of calculi

Determine causative agent of calculi

   
Calculi (Stone) Analysis with Photo 2005231
Method: Quantitative Reflectance Fourier Transform Infrared Spectroscopy/Quantitative Polarizing Microscopy

Determine composition of calculi

Determine causative agent of calculi

For specimens smaller than 2 mg, refer to Calculi (Stone) Analysis

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Evaluate for concomitant infection

Renal Function Panel 0020144
Method: Quantitative Chemiluminescent Immunoassay/Quantitative Enzyme-Linked Immunosorbent Assay

Evaluate for obstructive pathology

Panel includes albumin, calcium, carbon dioxide, creatinine, chloride, glucose, phosphorous, potassium, sodium, and BUN

Urinalysis, Complete 0020350
Method: Reflectance Spectrophotometry/Microscopy

Detect urinary tract abnormalities, including crystals

Urine Culture 0060131
Method: Culture/Identification

Evaluate for concomitant infection

Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic
Creatinine, 24-Hour Urine 0020473
Method: Quantitative Spectrophotometry
Oxalate, Urine 0020482
Method: Quantitative Spectrophotometry
Oxalate, Plasma 2011697
Method: Quantitative Spectrophotometry
Citric Acid, Urine 0020852
Method: Quantitative Enzymatic
Urea Nitrogen, Serum or Plasma 0020023
Method: Quantitative Spectrophotometry
Uric Acid, Serum or Plasma 0020026
Method: Quantitative Spectrophotometry
Calcium, Ionized, Serum 0020135
Method: Ion-Selective Electrode/pH Electrode
Parathyroid Hormone-Related Peptide (PTHrP) by LC-MS/MS, Plasma 2010677
Method: Quantitative High Performance Liquid Chromatography-Tandem Mass Spectrometry