Kidney Stones
Not one disease — what the stone is made of decides what prevents the next one
What it is
A kidney stone is a crystal that forms when the substances dissolved in urine become concentrated enough to come out of solution. About 8.8% of adults in the United States report having had one, more often men (10.6%) than women (7.1%), and more often people with obesity (11.2%) than people of normal weight (6.1%). But 'kidney stone' is a category, not a diagnosis. Roughly speaking, stones are calcium oxalate (the large majority), calcium phosphate, uric acid, struvite (formed by urine-splitting bacteria, and therefore an infection problem as much as a stone problem), or cystine (rare, genetic, and lifelong). These have different causes, different urine chemistries, and different prevention — which is why the most useful question after a stone is not 'how do I drink more water' but 'what was it made of, and why did it form'.
Why it matters
Stones recur. That is the fact the first episode rarely conveys: this is usually a chronic metabolic condition that announces itself as an acute event. The pain of passing one is what people remember, but the part that changes outcomes is what happens in the months afterward — whether the stone was analysed, whether the urine was measured, and whether prevention was matched to the cause rather than assumed. Two failures follow from skipping that. The first is under-treatment: 'drink more water' offered as a complete plan to someone whose real problem is a high sodium intake, a low urine citrate, or an undiagnosed metabolic cause. The second is the wrong treatment, and it is the one this page exists to correct: cutting out dietary calcium, which is intuitive, widely believed, and in a randomised trial made recurrence worse rather than better.
What BioSignal knows about treating this
What works for Kidney Stones
BioSignal’s clinical summary, most important first.
- Fluid intake sufficient to produce more than about 2-2.5 litres of urine a day — the one measure that applies to every stone type
- Normal dietary calcium with reduced sodium and reduced animal protein — better than a low-calcium diet in a randomised trial
- Potassium citrate where urine citrate is low or for uric acid stones (it raises urine pH and citrate)
- Thiazide diuretics for hypercalciuria — long-standing practice, but calibrated by a large placebo-controlled trial that found no benefit in unselected recurrent formers
- Allopurinol for recurrent calcium oxalate stones with high urinary uric acid
- Moderating oxalate only where it is genuinely high — and always paired with calcium at the same meal
- Urological treatment (shock-wave lithotripsy, ureteroscopy, percutaneous nephrolithotomy) for stones that will not pass or must not be left
Signal Records relevant to this condition
Interventions and contributing factors — some of these records describe a cause rather than a cure. The rating shown is BioSignal’s confidence in that Signal Record, not a claim about how well it treats this condition. Open any of them for the full evidence.
- Vitamin CHigh confidence
Does not prevent colds — one of the best-tested negatives in nutrition. Shortens them slightly, but only if you were already taking it. Megadoses are mostly excreted: absorption saturates around 200 mg/day. Genuinely useful for iron absorption, and genuinely essential — scurvy is still real.
- Vitamin DHigh confidence
Effective for deficiency and for bone health in at-risk groups. For broad disease prevention in adults who are already replete, the largest trials are null — and confidence in that null is high. Routine testing of healthy adults is not supported.
- MagnesiumModerate confidence
Genuinely effective for a few specific things — eclampsia (in hospital), constipation, migraine prevention, and a modest blood-pressure effect. The reasons most people actually buy it — sleep, cramps, anxiety — are the weakest part of the evidence.
New to this? Read these first
How this usually unfolds
- Recognize risk factors
- Get diagnosed
- Track key biomarkers
- Lifestyle first
- Evidence-based treatment
- Long-term monitoring
Who is at risk
- A previous stone — the single strongest predictor of the next one
- Low urine volume — from low fluid intake, hot climates, or heavy sweating
- High dietary sodium — it drives calcium into the urine
- High animal-protein intake — raises acid load and urinary calcium, lowers citrate
- Obesity and type 2 diabetes (uric acid stones especially — insulin resistance lowers urine pH)
- Family history
- Gout and high uric acid states
- Recurrent urinary infection with urea-splitting organisms (struvite)
- Inflammatory bowel disease, chronic diarrhoea, and bariatric surgery — via enteric hyperoxaluria
- Primary hyperparathyroidism and renal tubular acidosis (calcium phosphate)
- Cystinuria — an inherited cause presenting young
How it's diagnosed
In the acute episode, the question is whether there is a stone, where it is, and whether the kidney is obstructed or infected. Non-contrast CT is the most sensitive test; ultrasound is used first in pregnancy and often in younger patients to avoid radiation. But the diagnosis that changes the future is the metabolic one, and it happens after the pain stops. Two things are worth more than any imaging for preventing the next stone: analysis of the stone itself, if it can be caught, because composition dictates prevention; and a 24-hour urine collection, which measures volume, calcium, oxalate, citrate, uric acid, sodium and pH — the actual drivers. Guidelines reserve the full metabolic evaluation for recurrent stone formers and for first-time formers at higher risk (a solitary kidney, chronic kidney disease, bowel disease, children, or a stone type that is never idiopathic, such as cystine or struvite), rather than applying it to everyone after a single uncomplicated stone.
Key biomarkers
Lifestyle
Explore this condition across BioSignal
Related Foundations
Related body systems
Frequently asked questions
Should I avoid calcium to prevent calcium stones?
No — and this is the most important and most counter-intuitive thing on this page. It sounds obvious that a calcium stone should be prevented by eating less calcium, but the opposite is closer to the truth. Calcium in food binds oxalate in the gut, where the two leave the body together. Take the calcium away and that oxalate is absorbed instead, arrives at the kidney, and forms stones. This has been tested directly rather than argued: in a five-year randomised trial in men with recurrent calcium oxalate stones and high urinary calcium, a diet with normal calcium but low salt and low animal protein produced relapses in 12 of 60 men, compared with 23 of 60 on the traditional low-calcium diet — roughly half the risk (relative risk 0.49). Urinary oxalate rose in the low-calcium group and fell in the normal-calcium group, which is the mechanism made visible. Large observational cohorts point the same way: higher dietary calcium tracked with fewer stones in both men and women. One real distinction: dietary calcium and calcium supplements are not interchangeable. In women, dietary calcium was associated with lower risk while supplemental calcium was associated with higher risk — plausibly because supplements are often taken away from food, where they cannot do the oxalate-binding that makes food calcium protective. Do not cut the calcium in your diet. If you take a supplement, ask whether you need it, and take it with a meal.
Is drinking more water enough to prevent stones?
It is the foundation, and it is not the whole building. Fluid is the one intervention that helps every stone type, and it has been tested: in a five-year randomised trial of first-time stone formers, increasing water intake to produce more than two litres of urine a day roughly halved recurrence and lengthened the time to the next stone. So it earns its place first. But 'drink more water' fails as a complete plan for two reasons. It is not a volume of drinking, it is a volume of urine — 2 to 2.5 litres a day out, which in a hot climate or a physical job means considerably more in. And it does nothing about the other drivers: a high salt intake that keeps pushing calcium into the urine, a low urine citrate that removes the natural inhibitor of crystal formation, a uric acid stone forming because the urine is persistently acidic, or a metabolic cause such as hyperparathyroidism. Water is necessary. Whether it is sufficient is a question that only a stone analysis and a 24-hour urine can answer.
Does lemon juice or lemonade prevent kidney stones?
There is a real mechanism here, and the evidence is thinner than the enthusiasm. The logic is sound: citrate binds calcium in urine and inhibits crystals from forming and growing, and people who form stones often have low urinary citrate. Prescription potassium citrate works on exactly this principle, and a Cochrane review found that citrate salts reduce new stone formation and further growth of residual stones — while noting that the quality of the underlying trials is only moderate to poor. Lemon juice does raise urinary citrate. But 'lemonade therapy' has been studied mainly in small, short studies measuring urine chemistry rather than in trials measuring whether people got fewer stones, and the citrate delivered by a realistic amount of lemon juice is well below a prescription dose. There is a second trap: commercial lemonade brings sugar with it, which is not neutral for stone risk. The honest position is that lemon juice in water is a reasonable, harmless way to add fluid and some citrate, that it is not equivalent to potassium citrate, and that if your urine citrate is low, that is a finding to treat properly rather than to season.
Do thiazide diuretics prevent stones?
This is the calibration that changed most recently, and it deserves an honest answer rather than a confident one. Thiazides reduce urinary calcium, and they have been recommended for decades for recurrent calcium stones with high urinary calcium — the ACP and AUA guidelines both reflect that. Then NOSTONE, a large double-blind randomised trial, gave hydrochlorothiazide at 12.5 mg, 25 mg or 50 mg daily, or placebo, to 416 people with recurrent calcium-containing stones and followed them for a median of 2.9 years. Recurrence occurred in 59% on placebo, and in 59%, 56% and 49% on the three ascending doses, with no dose-response relationship and no statistically significant advantage at any dose. That is a genuinely negative result from a well-conducted trial, and it should not be explained away. Nor should it be over-read: NOSTONE enrolled recurrent stone formers generally rather than selecting for the high urinary calcium that thiazides are supposed to act on, so it is better read as evidence against giving thiazides to everyone with recurrent stones than as proof that they never help anyone. The result of all this is real uncertainty. Thiazides remain a reasonable option in selected people with demonstrated hypercalciuria, and the confident blanket recommendation they used to carry no longer matches the evidence.
Are all kidney stones the same?
No, and treating them as though they are is how prevention goes wrong. Calcium oxalate stones are the large majority and are the ones driven by urine volume, sodium, oxalate and citrate. Calcium phosphate stones tend to form in more alkaline urine and are more often linked to an underlying cause such as renal tubular acidosis or hyperparathyroidism. Uric acid stones form in persistently acidic urine, are strongly associated with obesity, insulin resistance and gout, and are unusual among stones in that they can sometimes be dissolved by alkalinising the urine rather than removed. Struvite stones are made by bacteria that split urea, which means they are an infection that must be cleared rather than a chemistry to be tuned; they can grow into large staghorn stones. Cystine stones come from an inherited transport defect, appear early in life, and need lifelong management. Same symptom, five different problems — which is the reason to keep the stone and have it analysed.
When is a kidney stone an emergency?
Renal colic is severe, but severity alone is not what makes it dangerous. The emergency is a stone that is both blocking a kidney and infected — an obstructed, infected system, which can progress to sepsis quickly and needs the kidney drained, not just antibiotics. The features that signal it are fever or chills alongside the pain. Get urgent care for pain with a fever or shaking chills, for pain with persistent vomiting that stops you keeping fluids down, if you are passing no urine at all, if you have only one working kidney (or a transplant) and think you have a stone, if you are pregnant, or for pain that is not controlled. BioSignal does not triage any of these, and a page is not the right place to work out which one you are having. Most stones pass without any of this happening — but 'most' is not a basis for waiting out a fever.
Evidence summary
Kidney stones affect roughly 8.8% of US adults and recur often enough to be treated as a chronic metabolic condition that presents acutely. Composition governs prevention — calcium oxalate, calcium phosphate, uric acid, struvite and cystine stones have different causes and different management — which is why stone analysis and, in recurrent or high-risk formers, a 24-hour urine collection are the investigations that change outcomes. Fluid intake sufficient to produce more than about 2 litres of urine daily is the one measure supported across stone types and is backed by a randomised trial in first-time formers; it is foundational but not a complete prevention plan. The most consequential misconception is dietary: restricting calcium to prevent calcium stones increases oxalate absorption and made outcomes worse in a five-year randomised trial, where a normal-calcium, low-sodium, low-animal-protein diet roughly halved recurrence (12/60 vs 23/60, RR 0.49) compared with a low-calcium diet. Dietary and supplemental calcium are not equivalent — supplements taken away from food were associated with higher risk in women, while dietary calcium was associated with lower risk. Citrate salts reduce recurrence and residual stone growth in a Cochrane review, though the underlying evidence is of moderate-to-poor quality; lemon juice shares the mechanism but not the dose, and 'lemonade therapy' rests on urine-chemistry studies rather than recurrence outcomes. Thiazides are the clearest example of live uncertainty: recommended for hypercalciuria by ACP and AUA guidance, but in NOSTONE (416 patients, median 2.9 years) hydrochlorothiazide showed no significant benefit over placebo at any of three doses and no dose-response — a negative result best read as evidence against unselected use rather than as proof of no effect in hypercalciuric patients. Allopurinol reduced recurrence in calcium oxalate formers with high urinary uric acid in a randomised trial. For acute ureteric stones, medical expulsive therapy is weaker than its adoption implies: in SUSPEND (1167 randomised), tamsulosin and nifedipine were no better than placebo at avoiding further intervention by four weeks. Surgical management follows current AUA guidance. This page covers stone disease; chronic kidney disease, urinary tract infection, and gout are separate objects, and visible blood in the urine is a red flag that requires assessment rather than a page.
References & sources
- Scales CD Jr, Smith AC, Hanley JM, Saigal CS (Urologic Diseases in America Project). Prevalence of kidney stones in the United States. Eur Urol 2012;62(1):160-165 (PMID 22498635; DOI 10.1016/j.eururo.2012.03.052)
- Pearle MS, Goldfarb DS, Assimos DG, et al. Medical management of kidney stones: AUA guideline. J Urol 2014;192(2):316-324 (PMID 24857648; DOI 10.1016/j.juro.2014.05.006)
- Qaseem A, Dallas P, Forciea MA, Starkey M, Denberg TD (Clinical Guidelines Committee of the American College of Physicians). Dietary and pharmacologic management to prevent recurrent nephrolithiasis in adults: a clinical practice guideline from the American College of Physicians. Ann Intern Med 2014;161(9):659-667 (PMID 25364887; DOI 10.7326/M13-2908)
- Fink HA, Wilt TJ, Eidman KE, et al. Medical management to prevent recurrent nephrolithiasis in adults: a systematic review for an American College of Physicians Clinical Guideline. Ann Intern Med 2013;158(7):535-543 (PMID 23546565; DOI 10.7326/0003-4819-158-7-201304020-00005)
- Pearle MS, Matlaga BR, Antonelli JA, et al. Surgical Management of Kidney and Ureteral Stones: AUA Guideline (2026) Part I: Evaluation and Treatment of Patients With Kidney and/or Ureteral Stones. J Urol 2026;215(2):113-123 (PMID 41263323; DOI 10.1097/JU.0000000000004842)
- Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328(12):833-838 (PMID 8441427)
- Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med 1997;126(7):497-504 (PMID 9092314)
- Borghi L, Schianchi T, Meschi T, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med 2002;346(2):77-84 (PMID 11784873)
- Borghi L, Meschi T, Amato F, Briganti A, Novarini A, Giannini A. Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study. J Urol 1996;155(3):839-843 (PMID 8583588)
- Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15(12):3225-3232 (PMID 15579526)
- Dhayat NA, Bonny O, Roth B, et al. (NOSTONE Study). Hydrochlorothiazide and prevention of kidney-stone recurrence. N Engl J Med 2023;388(9):781-791 (PMID 36856614; DOI 10.1056/NEJMoa2209275)
- Phillips R, Hanchanale VS, Myatt A, Somani B, Nabi G, Biyani CS. Citrate salts for preventing and treating calcium containing kidney stones in adults. Cochrane Database Syst Rev 2015;(10):CD010057 (PMID 26439475; DOI 10.1002/14651858.CD010057.pub2)
- Ettinger B, Tang A, Citron JT, Livermore B, Williams T. Randomized trial of allopurinol in the prevention of calcium oxalate calculi. N Engl J Med 1986;315(22):1386-1389 (PMID 3534570)
- Pickard R, Starr K, MacLennan G, et al. (SUSPEND Trial). Medical expulsive therapy in adults with ureteric colic: a multicentre, randomised, placebo-controlled trial. Lancet 2015;386(9991):341-349 (PMID 25998582; DOI 10.1016/S0140-6736(15)60933-3)
Educational information — not medical advice
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