The Stone Zone: Evaluation, Prevention, and Non-Surgical Management

Epidemiology, etc

1/11 (9%) people will make a stone (or more) in their lifetimes. After a stone episode, up to 50% will have another stone episode within 10yrs. Metabolic syndrome (obesity, HTN, DM) increase stone forming risks.

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. Has been shown to cut stone forming rate 27% -> 12% at 5yrs.
  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, which means a high acid load. All meat (mammal, bird, fish, etc) are equal, so cutting down on red meat is not enough.

Which fluids are best?

Water is best. Dark colas (contains phosphoric acid) are bad, and avoid other sugar-sweetened beverages. Caffeinated drinks (coffee, tea) are fine. Alcohol (wine, beer, etc) are fine.

Juices are good because citric acid -> citrate. Orange > lemon.

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: PMHx + Meds

Medical History

Medications

Mineral Metabolism Workup

Indications

Components

24hr Urine Findings and What to Do

Low Urine Volume

Hypercalciuria

Hyperoxaluria

Low Urine pH

Hypocitraturia

Medications

Thiazide Diuretics

Potassium Citrate (KCit)

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.

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