Stones: Evaluation, Prevention, and Non-Surgical Management

Rule, Andrew D., et al. "The ROKS nomogram for predicting a second symptomatic stone episode." Journal of the American Society of Nephrology 25.12 (2014): 2878-2886.

Epidemiology, etc

Stone Forming Factors

Oxalate: Component of most common stone type (CaOx). Only 20% come from diet, no benefit in avoiding oxalate-containing foods unless urine tests specifically show hyperoxaluria. Vitamin C (absorbic acid) is converted to oxalate, so high levels can increase stone formation.

Uric acid: can act as a nidus for CaOx stone formation. Urinary precipitation affected more by urinary acidification than uric acid levels.

Citrate: Main stone inhibitor. Inhibited by high acid foods (meat, cheese, eggs). Fruit and veggies contain the most citrate and have lowest acid load.

General Stone Prevention

  1. Drink more water: maintain UOP 2-3L to dilute salts and other stone forming agents, do not need to titrate to color
  2. Eat less salt: salt reabsorption in the tubule decreases calcium reabsorption, limit salt intake to < 2.3g daily (100mEq)
  3. Eat less meat: protein = amino acids -> high urinary acid load, all meat (mammal, bird, fish, etc) are equal, can also increase calcium excretion
  4. Oxalate-containing foods: only avoid if proven hyperoxaluria, likely due to enteric causes
  5. Vitamin C (absorbic acid): can be converted to oxalate, avoid high doses

Which fluids are best?

What's the deal with juice

  • Citrus juice contains citric acid, which is converted to citrate and bicarbonate
  • Grapefruit juice has the highest citrate level (197.5mEq/L)
  • Grapefruit and orange juice both contain potassium in addition to citrate, but lemon juice does not
  • Calcium supplements, yes/no?

    Decreased calcium leads to increased oxalate gut absorption. Calcium supplementation increases calcium stone risk. Therefore, take supplements only if low calcium to maintain the normal range.

    Workup after 1st Time Stone Formation

    Medical History

    Medications

    Mineral Metabolism Workup

    Indications

    Components

    Hypercalciuria

    24hr Urine Collection

    Measured variables

    Tips for Collection

    Management based on metabolic workup parameters

    Other random yet specific findings

    Medications

    Thiazide Diuretics

    Potassium Citrate (KCit)

    Calcium supplements

    Sodium Bicarbonate, Sodium Citrate

    Allopurinol

    alpha-mercaptopropionylglycine (Thiola)

    Acetohydroxamic acid

    Follow-Up

    Labs: repeat 24hr urine 6mo after initial assessment to check for improvements, then consider checking on annual basis to assess for adherence.

    Imaging: no clear evidence for long term screening, but most recommend annual KUB + renal US to assess for stone formation/growth and silent hydronephrosis.

    Important/Interesting Stone Studies

    Borghi 1996: Increased fluid intake (> 2L) decreases stone recurrence rates over 5 yrs compared to controls (27 vs 12%)

    Borghi 2002: low calcium diet versus low protein + low salt + moderate calcium, the moderate calcium diet had a 50% reduction in stone events compared to low calcium diet

    Lotan 2004: 1st time stone formers are most cost effectively managed w/ conservative therapy, but metabolic workup is more beneficial for recurrent stone formers

    Sources: