After the ER

Prevention that matches the evidence

Recurrence is the rule if nothing changes. The levers that keep showing up in trials are boring on purpose: urine volume, sodium, dietary calcium with meals, less animal protein, and citrate.

1. Drink until the urine is actually dilute

NIDDK: six to eight 8-ounce glasses as a floor, mostly water. Stone clinics usually aim for about 2.5 liters of urine a day — which means drinking more than that once you count sweat. Desert heat, shift work, and heavy exercise all raise the target. Pale straw is the visual check; a marked bottle is the behavioral check.

Helpful drinks: water, coffee in usual amounts, lemonade without a sugar dump. Unhelpful: sugar-sweetened soda as a habit. Grapefruit juice is the one citrus that stone papers often sidestep.

2. Cut sodium, not dietary calcium

Sodium pulls calcium into the urine. Stay near 2,000–2,300 mg of sodium a day. That is packaged food, restaurant food, and the salt shaker — not just “I don’t add salt.”

A five-year randomized trial in men with recurrent calcium oxalate stones found that a normal-calcium diet plus low salt and lower animal protein cut recurrence about in half versus a low-calcium diet. The low-calcium group leaked more oxalate. Bones also need the calcium.

Target: about 1,000–1,200 mg of calcium from food, taken with meals so it binds oxalate in the gut.

3. Animal protein in a smaller supporting role

Meat, organ meat, fish, and shellfish acidify urine and raise uric acid. That matters for uric acid stones and for calcium stones. You do not have to go vegan. You do have to stop treating every plate like a steakhouse.

4. Oxalate — moderate the high-load foods

Only if you form calcium oxalate stones or a 24-hour urine shows high oxalate. Pair leftover high-oxalate foods with calcium.

5. Citrate on purpose

Citrate binds calcium and is a crystallization inhibitor. Prescription potassium citrate is the drug version (FDA-approved for prevention). Food version: lemon juice. A small trial in hypocitraturic calcium-stone patients found ~85 mL of lemon juice a day raised urinary citrate about 2.5-fold — not as much as the drug, but in the same direction. Harvard clinicians often quote half a cup of lemon juice concentrate diluted through the day, or the juice of two lemons.

Medicines a clinic may add

• Thiazide diuretics to lower urinary calcium
• Potassium citrate (or potassium-magnesium citrate) for low citrate or acidic urine
• Allopurinol when uric acid in the urine is the driver
• Antibiotics plus surgery for struvite
• Specialty agents for cystinuria

Prevention tools