What Is a Kidney Stone? — A Grain of Sand Caught in the Waterway

Flank Pain That Arrives at Dawn

At dawn, one side of your flank suddenly begins to hurt. Whether you lie down, sit, or curl your body up, there is no comfortable position. The pain repeats waxing and waning, and can also radiate down toward the lower abdomen. One of the conditions that causes this kind of pain is a stone forming in the kidney (renal stone).

The kidneys are kidney-bean-shaped organs, one on each side in the upper back above the waist, that filter blood to send waste products and excess water out as urine. A kidney stone is a stone formed inside the kidney when substances dissolved in urine harden.

Stones are common and are counted as a major global health problem (PMID 40790363). The proportion of people suffering from stones varies greatly by region, with a 2017 international consensus review summarizing it as 7–13% in North America, 5–9% in Europe, and 1–5% in Asia (PMID 28213860). Over the past 50 years, it has increased substantially regardless of age, sex, or race (PMID 40790363). The age at which they form most frequently is 20–40 years, and a 2009 review noted that men outnumbered women by 3 to 2 (PMID 21565128). However, that gap is narrowing globally (PMID 28213860).

It is also common for stones to recur in someone who has experienced them once. The rate of recurrence within 5 years after having a first stone is estimated at 30–50% (PMID 38155376). The reason this condition is a heavy burden also lies chiefly in this frequent recurrence (PMID 40790363). Repeated stones can lead to kidney damage or infection spreading throughout the body (PMID 41871357).

This article looks in turn at where and how stones form, when pain arrives, how small and large stones are managed, and how far the evidence for preventing recurrence has accumulated.

The Waterway Where Urine Flows

Urine made in the kidneys travels a long path before exiting the body. The ureter is a thin tube that sends urine made in the kidneys to the bladder. The bladder is a muscular pouch that gathers urine and lets it out. The urethra is the final tube through which urine in the bladder goes out of the body.

This article compares this entire path to a water channel. Inside the kidney is a wide puddle-like space where the produced urine gathers, and from there a narrow water channel called the ureter leads to a reservoir called the bladder (PMID 27188687). Kidney stones form in this puddle-like space, sometimes floating around and sometimes stuck to the inner wall (PMID 27188687).

A grain of sand settled in the puddle does not block the flow of water. In fact, stones staying inside the kidney often pass without symptoms (PMID 26318710). However, even a stone inside the kidney tends to be removed if it grows, causes symptoms or a blockage, or if infections recur (PMID 30990297). The situation changes when the same grain of sand flows into the narrow water channel. A place arises where it gets caught, and water pools above the trapped spot.

There is something the sand grain analogy fails to capture. Because actual stones are grown from substances dissolved in urine that hardened inside the kidney, what was dissolved and how concentrated the urine was determine whether a stone forms and what kind it is (PMID 18486720).

Kidney stones are usually quiet while staying inside the kidney, and become a problem when they descend into the narrow ureter and get stuck.

Until What Was Dissolved Hardens Into Stone

More than 80% of stones are calcium-containing stones (PMID 38155376). That calcium was originally dissolved in the urine. There is a limit to how much can dissolve in water.

Supersaturation is a state where substances dissolved in urine exceed the limit of what can dissolve. The fundamental cause of all stones is that the urine becomes supersaturated with respect to the stone's components, and how much can remain dissolved depends on the urine volume, pH, and the total amount of substances excreted into the urine (PMID 18486720). A low urine volume and a shortage of water in the body are cited as common risks for all types of stones (PMID 36906146). When the same amount of substance is dissolved in less urine, it comes that much closer to the limit.

There is a substance that pairs with calcium. Oxalate is a substance found in plant-based foods like vegetables, nuts, fruits, and grains, and is also produced inside the body. Roughly half of the oxalate in a normal person's urine comes from food, and half from what is produced inside the body (PMID 30566003).

Calcium oxalate is a hardened crystal formed when calcium and oxalate meet in the urine, making up the most common component of kidney stones. Most stones have calcium oxalate as their main component, and many of those stones grow on top of calcium phosphate deposits spread across the inner tissue surface of the kidney (PMID 27188687). It resembles how a grain of sand grows larger on a small tray already laid out rather than on bare ground.

The common conditions that call forth calcium oxalate stones are four. They are excessive calcium excreted in the urine, excessive oxalate excreted, low citrate excreted, and a low urine volume (PMID 40790363). Hypercalciuria is a state where the calcium excreted in urine is higher than normal. It is the most common metabolic abnormality causing stones (PMID 21751520). Citrate is a substance that works in the urine to prevent calcium from hardening into stones. That is why a low excretion of citrate also falls under the risk conditions (PMID 40790363).

Aside from calcium-containing stones, there are a few more branches. Uric acid stones are stones formed when uric acid in the urine hardens, and they are deeply intertwined with the acidity of the urine. Calcium phosphate stones are also connected to the acidity of the urine (PMID 40790363). Beyond these, there are stones intertwined with specific bacterial infections and cystine stones arising from inherited genetic abnormalities (PMID 1962646; PMID 33910689). Cystine stones are the most common among stones arising from a single gene abnormality (PMID 33910689). Stones caused by medications account for 1 to 2% of all stones (PMID 29264783).

What calls forth stones has mostly emerged from observational studies. An observational study is research that does not tamper with people's lives, leaves them to live as they originally do, and watches what happens afterwards. An umbrella review re-analyzing 17 meta-analyses of such studies to weigh the evidence cited abdominal obesity, type 2 diabetes, gout, dietary salt, fructose intake, and hot climates as risk factors suggesting they may be causes (PMID 38814276). Association means they appear together, and does not contain proof that any single one is the cause.

Stones are substances dissolved in urine that have hardened past the limit, and the type of stone diverges depending on what has hardened.

When a Grain of Sand Blocks the Stream — Renal Colic

When a stone resting inside the kidney travels down the ureter with the urine, the story changes. Most people with stones visit the hospital because of the classic pain this causes (PMID 26318710).

Renal colic is a sudden, severe pain starting in the flank that occurs when a stone blocks the ureter. Acute renal colic caused by a stone blocking the urinary tract is treated as an emergency requiring immediate pain relief (PMID 26318710).

When a stone blocks the ureter, urine that cannot pass accumulates above it. Hydronephrosis is a condition where the inside of the kidney swells because urine cannot drain out. Therefore, one review recommends re-imaging within 14 days to check the stone's position and hydronephrosis even while waiting for the stone to pass on its own (PMID 30990297).

Pain occurs not when the stone forms, but when the stone travels down into the narrow ureter and blocks the urinary tract.

Pain relievers are chosen as the first drugs to manage pain. Nonsteroidal anti-inflammatory drugs are a group of pain relievers widely used to reduce pain, fever, and inflammation. The 2025 guidelines from the European Association of Urology (EAU) place this class as the first choice for pain management, with opioid analgesics as the next choice (PMID 40268592). Other reviews addressing renal colic in the emergency department also recommend the same direction (PMID 30990297; PMID 29939860). Which drug to use is decided by the medical staff considering the person's kidney function and circumstances. The burden that pain relievers place on the kidneys is followed up in "What Is Acute Kidney Injury? — A Tap That Suddenly Runs Dry, and Three Places to Look".

Diagnosis is confirmed with imaging. The same guidelines place ultrasound as the first test and low-radiation CT as the standard test to accurately view stones (PMID 40268592). A non-contrast CT almost never misses even small stones, and almost never mistakenly points to a stone when there is none (PMID 28966756). However, it has the limitation of radiation exposure (PMID 26318710). Urinalysis and urine culture are also performed together (PMID 30990297). During pregnancy, ultrasound is used as the primary imaging test (PMID 24515090).

There are cases that require haste. The first task when dealing with renal colic is to sort out whether the situation requires an immediate visit to the emergency room, and urinary tract infection is counted as a case where stones must be actively removed (PMID 30990297). Severe flank pain accompanied by fever is a signal that an infection may have overlapped with a blocked urinary tract, and it is a case that departs from waiting for stones to pass naturally, requiring prompt medical care. A review on stones in pregnant women also describes a situation where an obstruction is complicated by infection as a serious condition requiring immediate creation of a pathway for urine to drain (PMID 24515090). What fever, chills, and flank pain mean is followed up in "What Is a Urinary Tract Infection? — An Intruder Through the Gate, and When It Reaches the Keep".

Stones That Pass on Their Own, Stones Broken or Taken Out

Many small stones caught in the ureter pass out on their own. The 2016 guidelines of the European Association of Urology state that ureteral stones smaller than 6 mm can pass spontaneously in individuals without complicating factors and whose condition is well managed (PMID 26318710). Stones with a diameter smaller than 5 mm commonly exit the urinary tract, and cases requiring surgery are rare (PMID 28966756).

Expulsive therapy is a treatment using medication to help a stone inside the ureter pass on its own. It is summarized as mainly using drugs from the alpha-blocker class, which helps stones emerge and makes painkillers less necessary (PMID 26318710). However, this is only to the extent that there may be a benefit in stones larger than 5 mm in the lower ureter, the quality of studies testing this treatment is still rated as low, and it must be used with caution in children and pregnant women (PMID 29939860). The 2025 guidelines also stop at noting that this treatment can be considered for some selected individuals (PMID 40268592).

Not all stones are waited out. Having a urinary infection or a stone larger than 10 mm are counted as cases where the stone must be removed (PMID 30990297). Kidney stones without symptoms are watched through imaging, and the stone is removed if it grows, causes symptoms, blocks the urinary tract, or if infections repeat (PMID 30990297). Uric acid stones also have a path of being dissolved with oral medication (PMID 26318710).

The methods for removal are broadly three. Extracorporeal shock wave lithotripsy is a procedure that gathers and fires shock waves from outside the body to break stones into pieces. Ureteroscopy is a procedure that puts an endoscope through the urethra and bladder to go inside the ureter and kidney to break or take out stones. Percutaneous nephrolithotomy is a surgery that makes a small path in the skin of the flank to go inside the kidney to break and take out large stones. Which of the three to use is chosen by considering the size, location, and composition of the stone along with the person's circumstances (PMID 40268592). Ureteroscopy and percutaneous nephrolithotomy have high rates of leaving no stones behind (PMID 40790363). As the shift has moved from surgeries that open the belly widely to methods going in with endoscopes, the burden on the body has decreased, and the rate of leaving no stones behind and quality of life have improved (PMID 27188687).

There are also limits. A 2023 review noted that these procedures are expensive, can bring about acute kidney injury and a drop in kidney function, and do not prevent the possibility of new stones forming (PMID 38155376).

Even if you take out the stone, the conditions that made the stone remain just as they are.

Preventing Recurrence — Water, Diet, and the Evidence for Medication

Among dietary adjustments, water is the one backed by the longest follow-up in randomized trials. The effect of water was confirmed long ago in trials that split participants randomly to compare outcomes, whereas until around 2001, the benefits of other dietary modifications mostly relied on changes in urinary risk factors and observational studies (PMID 11224695). While the effect of water held up in long-term randomized trials, as of 2015 other dietary factors were often supported only by short-term studies (PMID 24938177). Which beverage is better—that is, the effects of tap water, mineral water, fruit juice, carbonated drinks, tea, and coffee—is still a matter of debate (PMID 34204863).

The most recent synthesis is a 2026 systematic review, which gathered 31 studies, 26 of which were randomized trials. In adults who suffered from calcium oxalate or calcium phosphate stones, evidence emerged that drinking more water and eating a diet with normal-to-generous calcium while keeping protein and salt low can reduce recurrence, but the certainty of this evidence was rated as low (PMID 41871357). The same analysis noted a lack of evidence regarding studies in children and potential harms, and reported that trials using lemon juice could increase mild adverse effects (PMID 41871357). In the evidence this article relies on, agents used to increase urinary citrate were medications, and there is no evidence to broaden this to mean people should consume lemon juice or food-grade citric acid. This evidence concerns the recurrence of stones in people who have already had them, and does not go so far as to imply that drinking lots of water improves overall kidney health.

There is a common misconception about calcium. Because it is a calcium-containing stone, it is easy to assume that calcium intake must be reduced, and the meta-analyses compiled above also note that the belief that calcium causes stones is widespread. Yet in that analysis, dietary calcium was actually identified as a factor leaning toward preventing stones (PMID 38814276). Restricting calcium is not helpful and may contribute to weakening bones (PMID 10593318), and syntheses also point out that eating too little calcium can increase urinary oxalate, which may actually trigger stones (PMID 21751520).

Oxalate is a little different. For individuals trying to reduce the growth of calcium oxalate stones, the authors of one review recommend drinking an appropriate amount of water, avoiding foods high in oxalate, and consuming sufficient calcium (PMID 30566003). This is the authors' recommendation, and a low-oxalate diet is not included in the list of interventions that a 2026 systematic review singled out as capable of reducing recurrence (PMID 41871357). This does not mean cutting out whole plant-based foods either. In an analysis pooling observational studies, a dietary pattern high in dietary fiber, vegetables, and fruit was instead identified as helping reduce stones (PMID 38814276).

Supplements must be viewed separately from dietary calcium. In an analysis pooling multiple observational studies, calcium supplementation and vitamin D did not increase risk, but what emerged as a protective factor was dietary calcium (PMID 38814276). Stones developing in conjunction with uncontrolled intake of calcium and vitamin D supplements have been reported (PMID 29264783), and a review summarizing kidney stone prevention notes that vitamin C and D supplements should be avoided (PMID 36906146). Evidence testing supplements in people who have had stones is absent from the systematic review this article relies upon.

The evidence for medication is in the same systematic review. In adults who suffered from calcium oxalate or calcium phosphate stones, evidence emerged that thiazide diuretics, drugs that shift urine toward an alkaline pH, and medications that reduce uric acid excreted in the urine can reduce recurrence, though the certainty of this evidence was also rated as low (PMID 41871357). These diuretics work by reducing the calcium excreted into the urine (PMID 21751520). One review recommends using such medications for individuals with recurrent calcium stones (PMID 30990297). In the same systematic review, these diuretics and uric acid-lowering drugs did not increase serious adverse effects, and this too had low certainty (PMID 41871357).

While evidence for reducing recurrence has accumulated around water, diet, and medication, most of it comes from adults with calcium stones, and the certainty of the evidence is rated as low.

Knowing the Composition of the Sand to Get Prevention Right

Prevention depends on the type of stone, and a tailored plan can be set only when you know the stone's composition along with the person's medical history and metabolic tests (PMID 39577887). Two tests serve as the starting point.

Stone composition analysis is a test to figure out what a passed or retrieved stone is made of. Stones caused by medications are confirmed by this analysis when the medication or its altered byproduct is found inside the stone (PMID 29264783).

A 24-hour urine test collects all the urine passed during a day to measure how much stone-related substances are being excreted. This test is usually used for people whose stones recur. The risk factors commonly revealed in such people are high amounts of calcium, oxalate, and uric acid, and low amounts of citrate, being excreted in the urine (PMID 10593318). One review recommends that everyone with stones have their recurrence risk assessed using medical history, basic tests, and imaging, and that those at high risk move on to more detailed metabolic testing (PMID 30990297).

The direction of prevention diverges depending on the composition. Uric acid stones are often treated with citrate-based medications (PMID 10593318). For cystine stones, the core of treatment is increasing urine volume and shifting the urine toward the alkaline side so that the cystine remains dissolved (PMID 33910689). People who do not absorb fat well due to intestinal disease excessively absorb the oxalate in their food, which increases urinary oxalate and raises the risk of stones (PMID 32900691). Because a stone can sometimes be a signal alerting to another disease in the body, a thorough evaluation is also used to find hidden metabolic abnormalities along with links to whole-body illness (PMID 40790363).

However, it has not been confirmed that choosing medications based on urine test results is always better. In a 2026 systematic review, there may have been no difference between medications chosen based on test results and medications used without testing, and even this conclusion was of low certainty of evidence (PMID 41871357). This comparison is about how medications are chosen and is a different question from the earlier point that the direction of prevention diverges when stone compositions differ. A 2001 review also noted that whether tailored treatment is better than non-tailored treatment requires further study (PMID 11224695).

Even if stones look the same, if their compositions differ, the direction of prevention changes, so prevention begins with knowing the type of stone. However, the evidence that choosing medications tailored through urine tests is better than using them uniformly is still weak.

The Path a Single Grain of Sand Took

We follow a single stone of one person from the beginning. Hot days continue, and the drinking water is little. High temperatures are cited as a risk factor for stones (PMID 38814276), and a small volume of urine is a common risk for all types of stones (PMID 36906146). Inside the kidney, calcium oxalate can harden beyond its limit, and stones can grow on small deposits on the tissue surface (PMID 27188687).

While the stone stays inside the kidney, usually nothing happens (PMID 26318710). Then, when the stone moves down into the ureter and gets stuck, renal colic strikes. At the hospital, doctors first screen whether the situation requires immediate emergency care, check for the stone with urinalysis and imaging, and manage the pain with nonsteroidal anti-inflammatory drugs (PMID 30990297). If an infection is superimposed, they lean toward removing the stone rather than waiting (PMID 30990297).

This person's stone was small, and there were no other problems like fever or infection. While waiting for it to pass naturally, they recheck with imaging within 14 days (PMID 30990297), and a few days later the stone comes out in the urine. When the retrieved stone is analyzed, it was calcium oxalate. The evidence on water, calcium, salt, and protein seen in the previous section came from people just like this, and its certainty was rated as low (PMID 41871357). If it had been a uric acid stone, the direction of prevention would be different (PMID 10593318).

Removing a grain of sand caught in the water channel and keeping the sand from building up again are different tasks. The second task begins with knowing what that sand is, and which prevention to choose is decided together with a doctor, considering the stone's composition, the number of recurrences, and other illnesses.

Where Else to Look

A stone may not end with just one stone. Stones are beginning to be regarded as a whole-body condition linked to an increased risk of chronic kidney disease, heart and vessel disease, metabolic syndrome, and low bone mass (PMID 40790363). Chronic kidney disease is a condition where the kidneys are injured or their function has declined for three months or longer. Chronic kidney disease itself is followed by "What Is Chronic Kidney Disease? — Lamps Going Out One by One, and the Load on Those Still Lit". The process by which the kidneys filter blood to make urine begins in "How Do the Kidneys Filter Blood? — A Sieve That Takes Almost Everything Back". Urinary tract infections that come with stones are taken up by "What Is a Urinary Tract Infection? — An Intruder Through the Gate, and When It Reaches the Keep", and the sudden decline in kidney function that can occur when a stone blocks the urinary tract or following a procedure is taken over by "What Is Acute Kidney Injury? — A Tap That Suddenly Runs Dry, and Three Places to Look".

Type 2 diabetes, cited as a risk factor associated with stones, can be seen in "What Is Diabetes? — The Letter That Never Comes, the Letter That Isn't Read". How to read in numbers the fact that CT almost never misses a stone is covered by "What a Test Actually Tells You — An Introduction to Sensitivity, Specificity, and Pretest Probability".

A 2025 review assesses that even though this condition is common and carries a heavy burden, it remains underrecognized, undercared for, and understudied (PMID 40790363). Most of the prevention evidence this article relies on comes from adults, and children's stones separately lack evidence (PMID 41871357).

Source Papers

• "Kidney stones." (2016) — PMID 27188687 — Stones originate as mineral deposits in the renal calyces and pelvis (floating or attached to the papillae), composed of crystals plus organic components, driven by supersaturation. Calcium oxalate is the main component, and many stones grow on top of calcium phosphate plaques. Recurrence reaches up to 50% within 5 years. The shift from open surgery to minimally invasive techniques has reduced morbidity and improved stone-free rates and quality of life.
• "Nephrolithiasis." (2008) — PMID 18486720 — The root cause of all stones is supersaturation (urine volume, pH, total solute excretion), with calcium stones being the most common.
• "Epidemiology of stone disease across the world." (2017) — PMID 28213860 — Prevalence is 7–13% in North America, 5–9% in Europe, and 1–5% in Asia. Prevalence is rising, the gender gap is narrowing, and randomized trials are lacking.
• "Kidney stone disease: risk factors, pathophysiology and management." (2025) — PMID 40790363 — This is a common and major global health problem that has increased over the past 50 years, with frequent recurrence being the main source of burden. It is a systemic condition linked to chronic kidney disease, cardiovascular disease, metabolic syndrome, and low bone mass. Calcium oxalate stones are associated with hypercalciuria, hyperoxaluria, hypocitraturia, and low urine volume, whereas uric acid and calcium phosphate stones are linked to urine pH. Evaluation uncovers hidden metabolic abnormalities and systemic disease associations. Ureteroscopy and percutaneous nephrolithotomy achieve high stone-free rates, yet the condition remains underrecognized and underresearched.
• "Kidney stones." (2009) — PMID 21565128 — Peak incidence occurs at ages 20–40, with a male-to-female ratio of 3:2 (summarized in 2009).
• "Urolithiasis: History, epidemiology, aetiologic factors and management." (2023) — PMID 38155376 — Affects 2–20% of the population, with a 5-year recurrence rate of 30–50%. Calcium stones account for over 80%. Procedures are expensive, can lead to acute kidney injury and functional decline, and do not prevent new stones.
• "EAU Guidelines on Diagnosis and Conservative Management of Urolithiasis." (2016) — PMID 26318710 — Most patients present with typical colic, while stones in the renal calyces are asymptomatic. Acute colic caused by ureteral stone obstruction is an emergency requiring immediate pain management. Low-dose CT carries radiation exposure limitations. Ureteral stones smaller than 6 mm often pass spontaneously in well-managed patients, and medical expulsive therapy aids passage and reduces the need for analgesics. Uric acid stones can be dissolved orally.
• "Kidney Stone Prevention." (2023) — PMID 36906146 — Low urine volume and dehydration are common risks for all stones. Dietary prevention strategies include avoiding vitamin C and D supplements.
• "Dietary oxalate and kidney stone formation." (2019) — PMID 30566003 — Oxalate comes from plant-based foods, with half of urinary oxalate derived from diet and half synthesized endogenously. To reduce calcium oxalate stone growth, the authors recommend hydration, avoiding high-oxalate foods, and consuming adequate calcium.
• "[Hypercalciuria]." (2011) — PMID 21751520 — Hypercalciuria is the most common metabolic abnormality. Citrate inhibits calcium stone formation, thiazides reduce urinary calcium, and a low-calcium diet can increase urinary oxalate and trigger stones.
• "Etiology and treatment of urolithiasis." (1991) — PMID 1962646 — Stone compositions include calcium oxalate, calcium phosphate, uric acid, magnesium ammonium phosphate (from urea-splitting bacterial infection), and cystine.
• "[Cystinuria]." (2021) — PMID 33910689 — This is the most common monogenic stone disease, centered on preventive treatment with high fluid intake and alkalinization (increasing urine volume and pH).
• "Drug-Induced Kidney Stones and Crystalline Nephropathy." (2018) — PMID 29264783 — Drug-induced stones account for 1–2% of the total. Stone analysis is necessary to identify drugs and metabolites. This serves as an example of metabolic stones caused by unregulated calcium and vitamin D supplements.
• "Risk factors for nephrolithiasis formation: an umbrella review." (2024) — PMID 38814276 — Out of 17 meta-analyses covering 46 factors, causative risk factors include abdominal obesity, type 2 diabetes, gout, dietary sodium, fructose, and high ambient temperature. Calcium supplements, dietary calcium, and vitamin D were widely believed to be causes, but show no difference or even lower risk. Dietary fiber and the DASH diet lean toward protection. The conclusion's list of protective factors includes dietary calcium and the DASH diet.
• "Kidney Stones: Treatment and Prevention." (2019) — PMID 30990297 — In renal colic, first rule out situations requiring emergency referral. Pain relief prioritizes nonsteroidal anti-inflammatory drugs, accompanied by urinalysis, cultures, and imaging. Infection or stones larger than 10 mm require active removal. Follow-up imaging within 14 days checks position and hydronephrosis. Asymptomatic stones are monitored via imaging and removed if they grow, cause symptoms or obstruction, or lead to repeated infections. All patients are screened for recurrence risk, recurrent calcium stones are treated with thiazides, allopurinol, or citrate, and high-risk cases undergo further metabolic evaluation.
• "European Association of Urology Guidelines on the Diagnosis and Treatment of Urolithiasis." (2025) — PMID 40268592 — Ultrasound is the first-line imaging modality and low-dose CT is the reference standard. Nonsteroidal anti-inflammatory drugs are first-line and opioids second-line. Alpha-blocker medical expulsive therapy is considered for selected patients. Shock wave lithotripsy, ureteroscopy, and percutaneous nephrolithotomy are the main procedures, chosen based on stone and patient characteristics.
• "Medical treatment of urinary stones." (2018) — PMID 29939860 — Nonsteroidal anti-inflammatory drugs are prioritized for acute colic, alpha-blockers may benefit distal ureteral stones larger than 5 mm, trials on medical expulsive therapy have low quality, and caution is required in children and pregnant women.
• "Preventive Kidney Stones: Continue Medical Education." (2017) — PMID 28966756 — Unenhanced CT achieves a sensitivity and specificity of nearly 100% even for small stones. Stones under 5 mm frequently pass spontaneously, and surgery is rarely needed.
• "Kidney stones during pregnancy." (2014) — PMID 24515090 — Ultrasound is the first-line imaging modality during pregnancy, and obstructing stones complicated by infection represent a serious condition requiring immediate drainage.
• "Prevention of Recurrent Nephrolithiasis in Adults and Children: A Systematic Review." (2026) — PMID 41871357 — Across 31 studies (26 randomized), in adults with calcium oxalate or calcium phosphate stones, increased fluid intake, moderate-to-high calcium, low protein, low sodium diets, thiazides, alkali, and allopurinol may reduce recurrence (low certainty). Tailored versus empirical medication may show no difference (low certainty). Lemon juice has mild side effects, and thiazides and allopurinol do not increase serious adverse events (low certainty). Evidence for other interventions, such as oxalate restriction, is limited. Recurrent stones can lead to kidney injury and sepsis, and evidence for children and harms is lacking.
• "Prevention of nephrolithiasis." (2001) — PMID 11224695 — The efficacy of high fluid intake is validated by randomized trials, whereas other dietary measures rely on urinary risk factors and observational studies. Tailored versus untailored treatments require further study.
• "Diet: from food to stone." (2015) — PMID 24938177 — High fluid intake shows sustained efficacy in long-term randomized trials, while other dietary factors are inferred only from short-term studies.
• "Nutrition and Kidney Stone Disease." (2021) — PMID 34204863 — Inadequate fluid intake is the primary dietary risk factor, and the effects of specific beverage types remain debated.
• "Prevention of recurrent nephrolithiasis." (1999) — PMID 10593318 — Calcium restriction is useless and may contribute to osteoporosis. 24-hour urine testing is typically performed in recurrent patients. Major risk factors include hypercalciuria, hyperoxaluria, hypocitraturia, and hyperuricosuria, and uric acid stones are frequently treated with citrate supplementation.
• "Nephrolithiasis." (2024) — PMID 39577887 — Because prevention varies by stone type, stone composition, medical history, and metabolic evaluation are necessary.
• "Pathophysiology and Treatment of Enteric Hyperoxaluria." (2021) — PMID 32900691 — Fat malabsorption leads to enhanced oxalate absorption and increased urinary oxalate, elevating stone risk.