Kidney stones announce themselves without warning. One moment you feel fine; the next, a wave of pain grips your flank and will not let go. Roughly one in ten Americans forms a urinary stone, and people who have had both rate the pain as worse than childbirth.
What most people never hear matters most: passing a stone is the beginning of the story, not the end. Without a prevention plan, about half of stone formers produce another within five to ten years. That is not fate. Most people leave the emergency room with pain relief and a strainer, never getting the lab testing that explains why.
What are kidney stones?
A kidney stone is a hard crystalline mass that forms when minerals in urine become too concentrated to stay dissolved. Urine is a solution with limits: when calcium, oxalate, uric acid or phosphate exceed what the water can hold, they crystallize, stick together and grow.
Two forces decide this: how concentrated the urine is, and how much inhibitor it holds. Citrate is the main one, binding calcium so it cannot pair with oxalate. Acidity matters as much, since uric acid crystallizes in acidic urine while calcium phosphate and struvite prefer alkaline urine. Prevention therefore starts with a urine pH measurement taken across a full day rather than a single moment.
Stones sitting in the kidney often cause nothing. Trouble starts when one enters the ureter, the narrow tube from kidney to bladder: flow is blocked, pressure backs up, and renal colic follows.
Symptoms and what renal colic feels like
Renal colic is not a steady ache. It arrives in waves of twenty minutes to an hour, eases, then returns. It begins in the flank between the lower ribs and the hip and radiates toward the groin as the stone descends. Crucially, no position relieves it: people with renal colic pace and rock and cannot sit still, unlike back strain, where lying still helps.
Blood in the urine, nausea, vomiting and urgent small-volume urination as the stone nears the bladder are all common. Cloudy or foul-smelling urine suggests infection alongside the stone.
Fever with stone pain is a medical emergency
Stone pain with fever or chills means going to an emergency department immediately. It suggests an infected, obstructed kidney: urine trapped behind a blocked ureter becomes a closed reservoir where bacteria multiply with nowhere to drain. Antibiotics alone cannot fix it, because they cannot reach an obstructed system, and pressure drives bacteria into the bloodstream. This can progress to a life-threatening bloodstream infection that overwhelms the organs within hours. Treatment requires urgent drainage, usually a stent or a tube through the skin, plus intravenous antibiotics. Do not wait until morning.
Other red flags that mean the emergency room
- Inability to pass urine at all.
- Vomiting you cannot control, so fluids and medication will not stay down.
- Pain home measures cannot manage, or that escalates despite medication.
- A single functioning kidney, a transplant, or known kidney disease.
- Pain during pregnancy, which changes imaging and treatment decisions.
Types of kidney stone
| Stone type | How common | What drives it | What helps prevent it |
|---|---|---|---|
| Calcium oxalate | Large majority of stones | Low urine volume, high calcium and oxalate, low citrate, high sodium | Fluid, less sodium, normal dietary calcium with meals |
| Calcium phosphate | Roughly one in ten | Alkaline urine, high urinary calcium, renal tubular acidosis | Treating the cause, lowering sodium, supervised alkali therapy |
| Uric acid | Around one in ten, rising with obesity | Acidic urine, low volume, animal protein, insulin resistance | Raising urine pH, more fluid, less animal protein |
| Struvite | Under one in ten, more often in women | Chronic infection with urea-splitting bacteria | Complete surgical removal plus eradicating the infection |
| Cystine | Rare, about one in a hundred stone formers | Inherited transport defect leaking cystine into urine | High fluid intake day and night, alkalinization, thiol-binding drugs |
Causes and risk factors
Low urine volume is the common denominator across nearly every stone type. Heat, heavy labor, endurance exercise, chronic diarrhea or drinking little all concentrate urine, which is why stone incidence rises in summer and in hot states.
Diet contributes in counterintuitive ways. High sodium is a major driver, because the kidney excretes calcium alongside sodium, so a salty diet pushes calcium into urine however much calcium you eat. Heavy animal protein acidifies urine, raises uric acid and lowers citrate. Sugar-sweetened drinks increase risk; coffee, tea and citrus juices do not.
History carries real weight: one stone roughly doubles the odds of another, and a first-degree relative raises risk independently. Obesity, type 2 diabetes, high blood pressure and gout all increase formation, as do certain antiseizure and antiretroviral drugs, high-dose vitamin C, and variants such as a horseshoe kidney where urine pools.
How kidney stones are diagnosed
During an acute episode, imaging answers whether a stone is present, how big it is and where it sits. Low-dose non-contrast computed tomography is the most accurate test, while ultrasound uses no radiation and comes first in pregnancy, children and increasingly adults.
Urinalysis looks for blood, infection, and the microscopic crystal types that hint at what a stone is made of. Bacteria plus a raised white blood cell count in the urine sample changes management entirely and points toward urgent drainage.
The metabolic workup: the tests that drive prevention
All of the above is emergency medicine. The testing that prevents the next stone happens weeks later, once you are back to your usual diet. This panel identifies which chemical abnormality produces your stones and gives you numbers to re-measure later.
| Test | What it measures | What an abnormal result points to |
|---|---|---|
| Stone composition analysis | Mineral makeup of a passed or removed stone | Directs the whole strategy: cystine means an inherited disorder, struvite chronic infection |
| 24-hour urine volume | Total urine produced across a full day | The commonest and most correctable abnormality; it concentrates every other risk factor |
| 24-hour urine calcium | Calcium your kidneys excrete daily | Excess dietary sodium, a renal calcium leak, or overactive parathyroids |
| 24-hour urine oxalate | Daily oxalate output | Heavy oxalate intake, malabsorption after bowel disease or bariatric surgery |
| 24-hour urine citrate | The urine’s main natural crystal inhibitor | Chronic acid load from animal protein, potassium depletion, or diarrhea |
| 24-hour urine uric acid | Daily uric acid excretion | High purine intake or gout; favors uric acid stones |
| 24-hour urine sodium | An objective record of your real salt intake | Explains high urinary calcium and is the easiest lever to pull first |
| Urine pH | How acidic or alkaline your urine is | Low pH favors uric acid stones; high pH favors calcium phosphate and struvite |
| Serum calcium | Calcium circulating in the blood | Elevation alongside stones is the classic clue to primary hyperparathyroidism |
| Parathyroid hormone | The hormone governing calcium balance | Raised PTH with high blood calcium confirms a curable cause of recurrent stones |
| Serum uric acid | Uric acid in the bloodstream | Links stones to gout and metabolic syndrome; may prompt urate-lowering treatment |
| Creatinine and eGFR | Overall kidney filtering performance | A falling eGFR signals damage from repeated obstruction and limits which drugs are safe |
Collect the 24-hour urine while eating your normal diet, because the goal is your real chemistry, and repeat it a few months after starting a plan. Alongside it, review the creatinine and eGFR values that show how well your kidneys filter waste.
Treatment: passing, removing, relieving
Most stones under about five millimeters pass on their own within a few weeks; management aims at getting you through that window safely.
Fluids come first, though heroic volumes do not push a stone out faster. For pain, nonsteroidal anti-inflammatory drugs are first-line because they reduce ureteral inflammation and pressure as well as blunting pain, with opioids kept for cases where NSAIDs are unsuitable. Antiemetics control nausea so fluids stay down.
Medical expulsive therapy uses alpha-blockers, which relax smooth muscle in the lower ureter. The benefit is modest and concentrated in larger stones low down, so it is offered selectively.
When a stone will not pass, three procedures dominate. Shock wave lithotripsy fragments it with focused acoustic energy from outside the body, working less well on very hard stones. Ureteroscopy passes a fine telescope through the bladder so the stone can be lasered or basketed out, clearing most stones in one session. Percutaneous nephrolithotomy makes a small tract through the flank into the kidney and is standard for large or staghorn stones. A temporary stent is often left afterward.
Preventing the next stone
Fluid intake is the single highest-yield preventive measure, and nothing else comes close. Raising urine volume dilutes every crystallizing substance at once, which is why it works across all stone types. Drink enough that your urine stays pale straw-colored all day, with more in heat or after exercise; your clinician can set a target volume from your 24-hour result.
Sodium reduction comes next and is more powerful than most people expect, since cutting salt directly lowers urinary calcium; most dietary sodium comes from processed and restaurant food, not the shaker. Moderating animal protein reduces acid load and preserves citrate. For calcium oxalate formers, trimming the heaviest oxalate sources such as spinach, rhubarb, beets and almonds helps, though rarely alone.
The calcium myth, corrected
The most damaging misconception in stone prevention is that people with calcium stones should avoid dietary calcium. The opposite is true. Calcium eaten with a meal binds oxalate inside the intestine, forming a compound that leaves in stool. Cut it and more free oxalate is absorbed, urinary oxalate rises, and stone risk goes up. Randomized evidence shows normal calcium with reduced sodium and animal protein prevents recurrence better than a low-calcium diet. Supplements are separate, since taken apart from food they may raise risk, so anyone considering them should first review a total calcium blood measurement that shows where their circulating level sits.
Citrate can be raised through citrus fruits and juices and, when urinary citrate is low, through prescription alkali therapy. Where diet falls short, medication follows stone type: thiazide diuretics to lower urinary calcium, alkali citrate for acidic urine, urate-lowering agents for uric acid stones. None replaces the fluid and dietary foundation.
When stones signal something else
Sometimes a stone is the visible symptom of systemic disease. Primary hyperparathyroidism is the classic example: an overactive gland raises blood calcium, floods the urine with it, and produces stones no diet will fix. Detection depends on measuring calcium and the parathyroid hormone level that governs how calcium moves between bone, gut and kidney together. Surgery cures it.
Uric acid stones frequently accompany gout and the persistently high urate that drives its joint attacks, since both trace back to acidic urine.
Inflammatory bowel disease and bowel resection cause enteric hyperoxaluria: unabsorbed fat binds calcium in the gut, leaving oxalate free to be absorbed, while diarrhea strips fluid and citrate. Anyone living with the malabsorption that Crohn’s disease produces in the small intestine faces markedly higher risk, and bariatric surgery creates the same chemistry. Cystinuria should be suspected whenever stones start in childhood or recur relentlessly.
Latest scientific advances
A Swiss trial tested a long-standing assumption about thiazide diuretics, blood pressure drugs used for decades to reduce urinary calcium. Researchers randomly assigned 416 adults with recurrent calcium stones to one of three hydrochlorothiazide doses or placebo, following them a median of 2.9 years. Recurrence occurred in 59% of the placebo group and 49% to 59% of treated groups, with no dose-response relationship, while low potassium, new gout and new diabetes were more frequent on the drug (Dhayat et al., 2023). What this means for you: medication is not an automatic answer, and anchoring prevention in fluid, diet and repeat urine testing matters more than ever.
A phase 2 crossover trial examined empagliflozin, a diabetes drug that makes the kidneys excrete glucose. Fifty-three adults without diabetes who had formed calcium or uric acid stones took the drug and placebo for two weeks each in random order, while researchers measured urine supersaturation ratios, a validated marker of how close urine is to crystallizing. Calcium phosphate supersaturation fell 36% versus placebo in calcium stone formers, and uric acid supersaturation fell 30% in uric acid stone formers (Anderegg et al., 2025). What this means for you: an established drug class may become a prevention option, though larger trials are needed.
The European Association of Urology issued updated urolithiasis guidelines synthesizing current evidence. They name ultrasound the first-line imaging test and low-dose CT the reference standard, put nonsteroidal anti-inflammatory drugs first for pain with opioids second, endorse alpha-blocker expulsive therapy for selected ureteral stones, and recommend genetic testing for high-risk patients (Skolarikos et al., 2025). What this means for you: best practice individualizes imaging and treatment by stone size, location and composition.
Myths and facts
- Myth: cutting calcium prevents calcium stones. Fact: normal dietary calcium with meals binds oxalate and lowers risk.
- Myth: beer flushes a stone out. Fact: no drink dislodges a lodged stone, and alcohol dehydrates.
- Myth: passing one stone means it is over. Fact: about half of stone formers recur within five to ten years.
- Myth: pain always means a stone is moving. Fact: large kidney stones can be silent while small mobile ones are agonizing.
Glossary
| Term | Meaning |
|---|---|
| Nephrolithiasis | The medical term for kidney stone disease. |
| Renal colic | Wave-like flank pain from a stone obstructing the ureter. |
| Ureter | The narrow tube carrying urine from kidney to bladder. |
| Supersaturation | When urine holds more mineral than it can keep dissolved. |
| Citrate | A urinary substance that binds calcium and inhibits crystals. |
| Hyperoxaluria | Excess oxalate in urine from diet, malabsorption or genetics. |
| Staghorn stone | A large branching stone filling the kidney. |
| Lithotripsy | Breaking a stone up with focused shock waves. |
| Ureteral stent | A soft temporary tube keeping the ureter draining. |
Frequently asked questions
What causes kidney stones?
Stones form when urine becomes concentrated enough that minerals crystallize instead of staying dissolved. The commonest contributor is low urine volume from drinking too little or losing fluid through heat, exercise or diarrhea. High sodium pushes calcium into urine, heavy animal protein raises acid and uric acid while lowering citrate, and low citrate removes the brake on crystal growth. Obesity, diabetes, gout, bowel disease and family history add risk.
How do I know if I have a kidney stone?
The hallmark is sudden severe flank pain that comes in waves, radiates toward the groin, and does not ease in any position. Blood in the urine, nausea, vomiting and urgent frequent urination often accompany it. Confirmation needs imaging, usually low-dose CT or ultrasound. If pain comes with fever, chills or an inability to urinate, seek emergency care immediately.
How long does it take to pass a kidney stone?
Size and location decide it. Stones under four millimeters usually pass within one to two weeks; stones of five to six millimeters may take several weeks and pass less reliably. Stones larger than about seven millimeters often need a procedure, and stones already low in the ureter pass sooner. Your clinician may add an alpha-blocker for selected larger stones.
Can kidney stones cause permanent kidney damage?
A single stone that passes promptly rarely causes lasting harm. Risk rises with prolonged obstruction, repeated episodes, infection stones, or a single kidney. Persistent blockage raises pressure inside the kidney and gradually reduces filtering capacity, and repeated infections accelerate that damage. This is why fever plus stone pain demands emergency drainage and why recurrent stone formers need kidney function tracked.
Should I save the stone I pass?
Yes, and it is among the most useful things you can do. Strain your urine and keep any fragment in a clean dry container rather than tape or tissue. Analysis identifies the composition, which determines your whole prevention strategy: uric acid calls for raising urine pH, struvite means eradicating an infection, cystine indicates an inherited disorder. Without it, prevention is guesswork.
Sources
- NIDDK — Kidney Stones — National Institutes of Health, 2025 — niddk.nih.gov
- MedlinePlus — Kidney Stones — U.S. National Library of Medicine, 2025 — medlineplus.gov
- Mayo Clinic — Kidney stones — Mayo Foundation for Medical Education and Research, 2025 — mayoclinic.org
- Dhayat NA, et al. — Hydrochlorothiazide and Prevention of Kidney-Stone Recurrence — New England Journal of Medicine, 2023 — doi.org
- Anderegg MA, et al. — Empagliflozin in nondiabetic individuals with calcium and uric acid kidney stones: a randomized phase 2 trial — Nature Medicine, 2025 — doi.org
- Skolarikos A, et al. — European Association of Urology Guidelines on the Diagnosis and Treatment of Urolithiasis — European Urology, 2025 — doi.org
Further reading
- Repeated obstruction erodes filtering capacity, so understand how chronic kidney disease develops.
- Blood urate ties stones to metabolic health, so read what a uric acid blood test indicates.
- Urine tells a different story from blood, so review how urinary uric acid is interpreted.
- Malabsorption depletes crystal-inhibiting minerals, so learn what a magnesium blood level reveals.
Understand your lab results with BloodSense
Stone prevention is a numbers game, and the numbers are yours. A stone-prevention panel combines the 24-hour urine measurements of calcium, oxalate, citrate, uric acid, sodium, volume and pH with the blood work revealing systemic causes: calcium, parathyroid hormone, uric acid, creatinine and eGFR.
BloodSense turns those results into plain language, showing which values sit outside range, what each suggests, and which questions to bring to your urologist. Repeat the panel a few months later and you see the effect in the numbers instead of waiting for the next attack.
