Kidney Stones

Kidney stones are hard deposits formed from crystals within urine. A stone entering the ureter can cause severe loin to groin pain, nausea and blood in the urine. Most small uncomplicated stones pass, but infection behind an obstruction, absent urine, uncontrolled symptoms or obstruction of a solitary kidney requires urgent urological treatment.

What kidney stones are Kidney stones are hard deposits that form when substances within urine crystallise and grow together. The medical term for a urinary stone is a calculus. Kidney stone disease is also called urolithiasis or nephrolithiasis. A stone can remain within the kidney without causing symptoms. It becomes particularly painful when it moves into the ureter and obstructs urine flow. Stone disease is not one disorder with one cause. Different stone compositions arise from different combinations of urine concentration, acidity, infection, metabolism, medicines and inherited factors. The urinary tract Your kidneys filter blood and produce urine. Urine drains from each kidney through a narrow muscular tube called a ureter. The ureters enter the bladder, which stores urine until it leaves through the urethra. A stone can be located within a kidney, ureter, bladder or urethra. This lesson focuses mainly on kidney and ureteric stones. The location matters because a small ureteric stone can cause intense pain, while a larger non obstructing kidney stone may remain silent. How crystals become stones Urine contains dissolved minerals, salts and metabolic waste products. When urine becomes too concentrated, some substances exceed the amount that can remain dissolved. This state is called supersaturation. Tiny crystals can then form, remain in the kidney and grow as more material deposits on their surface. Natural inhibitors, including citrate, help prevent crystal growth. Low urine volume, high concentrations of stone forming chemicals or reduced inhibitors can shift the balance towards stone formation. Concentration is only part of the explanation Dehydration is important because less water leaves the same amount of dissolved material in a smaller urine volume. Urine acidity also matters. Uric acid and cystine are less soluble in acidic urine, while calcium phosphate and infection stones are favoured by more alkaline urine. Anatomical narrowing or poor urine drainage can allow crystals to remain and enlarge. Many people have several contributing factors rather than one single cause. Calcium oxalate stones Calcium based stones are the commonest group, and calcium oxalate is the commonest stone composition overall. Oxalate comes from normal metabolism and from some foods. Calcium and oxalate can combine when urine becomes supersaturated. Risk can rise with high urinary calcium, low citrate, low urine volume or excessive oxalate absorption from the bowel. A calcium oxalate stone does not usually mean that dietary calcium should be removed. Normal dietary calcium can bind oxalate within the bowel and reduce its absorption. Calcium phosphate stones Calcium phosphate stones are less common than calcium oxalate stones and may occur alone or within a mixed calcium stone. They are associated with more alkaline urine. Distal renal tubular acidosis and some urinary infections can contribute. Primary hyperparathyroidism can raise blood and urine calcium and increase calcium stone risk. Some calcium phosphate forms, including brushite, can be hard and less responsive to shockwave treatment. Uric acid stones Uric acid stones form mainly in persistently acidic urine. They are associated with metabolic syndrome, obesity, type 2 diabetes, gout, high uric acid turnover and some diets high in animal protein. A normal blood urate does not exclude a uric acid stone because urine acidity is often the central factor. Uric acid stones are usually visible on non contrast CT but may not appear on an ordinary plain X ray. Unlike most stones, they can sometimes be dissolved through carefully monitored urine alkalinisation. Struvite or infection stones Struvite stones contain magnesium ammonium phosphate and are associated with infection by bacteria that split urea. These bacteria make urine more alkaline and create conditions in which infection stones grow. A struvite stone can enlarge rapidly and form a branching staghorn calculus that fills much of the kidney collecting system. Antibiotics alone may not eradicate infection while infected stone material remains. Treatment usually requires infection control and removal of as much stone as safely possible. Cystine stones Cystine stones result from cystinuria, an inherited disorder affecting transport of certain amino acids through the kidneys and bowel. Cystine is poorly soluble, particularly in acidic urine. Stones often begin in childhood or early adulthood and can recur frequently. The diagnosis affects family counselling and long term prevention. Management may require very high fluid intake, urine alkalinisation and specialist medicines. Cystine stones are relatively hard and can be more difficult to fragment with shockwaves. Mixed stones and uncommon types Many stones contain more than one mineral. Stone analysis reports the main and secondary components. Rare stones include xanthine, 2,8 dihydroxyadenine and ammonium urate stones. Some indicate an inherited metabolic disorder. Blood clots, fungal material and foreign bodies can occasionally act as a centre around which deposits form. An unusual composition, early onset or repeated bilateral stones should prompt specialist metabolic or genetic assessment. Medicine related stones Some medicines crystallise directly within urine. Examples include indinavir, atazanavir, triamterene and selected sulfonamide medicines. Other medicines change urine chemistry rather than becoming part of the stone. Topiramate and acetazolamide can raise urine pH and reduce citrate, increasing calcium phosphate risk. Excess vitamin C can increase oxalate production in some circumstances. Excess calcium or vitamin D can contribute when they cause high urine calcium. Necessary medicines should not be stopped independently. The indication, dose, alternatives and prevention plan require a clinical review. Dehydration is a major modifiable risk Low urine volume is one of the most important preventable contributors to stone formation. Risk rises in hot climates, hot workplaces, during endurance activity and when access to drinks or toilets is limited. Vomiting, diarrhoea, fever and fasting can temporarily concentrate urine. A pale urine colour often suggests reasonable hydration, although vitamins, medicines and disease can alter colour. Climate and occupation People living or working in hot environments lose more water through sweat. Outdoor workers, drivers, healthcare staff and others who delay drinking or urination may produce concentrated urine for long periods. Stone prevention therefore involves access to water and practical opportunities to drink and use a toilet. Advice must account for heart failure, advanced kidney disease or another condition requiring fluid restriction. Family history and inherited susceptibility Kidney stones often run in families. Shared genes can affect urine calcium, oxalate, citrate, uric acid or cystine. Families may also share diet, climate and hydration patterns. A strong family history is particularly relevant when stones begin young, recur quickly or occur in both kidneys. Family history increases risk but does not determine that stones are inevitable. Previous stones A previous stone is one of the strongest predictors of another episode. Recurrence does not mean that treatment failed. It may reflect persistent urine chemistry, incomplete stone clearance or new risk factors. The time to recurrence, number of stones and need for procedures help classify future risk. Prevention becomes increasingly important after repeated episodes because each obstruction or intervention carries potential harm. Body weight and metabolic syndrome Obesity, insulin resistance, hypertension and type 2 diabetes are associated with stone disease. Insulin resistance can reduce ammonium handling and make urine more acidic, increasing uric acid stone risk. Dietary patterns high in sodium, refined sugar and excess animal protein may add to risk in some people. Weight advice should remain proportionate and non judgemental. Genetics, medicines, mobility, income and food access all influence body weight and stone risk. Dietary sodium A high sodium intake increases urinary calcium excretion in many people. It can reduce the benefit of thiazide treatment and contribute to hypertension. NICE advises adults with stones to keep total salt intake at no more than 6 grams daily. Most dietary salt comes from processed and prepared foods rather than salt added at the table. Dietary calcium Restricting ordinary dietary calcium can increase calcium oxalate stone risk by leaving more oxalate free for absorption. NICE advises maintaining a normal adult calcium intake, generally 700 to 1,200 milligrams daily. Calcium obtained with meals from food differs from taking large supplement doses away from meals. Supplements may still be appropriate for bone health or deficiency, but the timing and dose should be reviewed in recurrent stone formers. Oxalate and food Oxalate is present in foods such as spinach, rhubarb, beetroot, nuts and some chocolate products. Most people do not need an extremely restrictive low oxalate diet after one stone. Targeted reduction is more useful when stone analysis and urine testing show calcium oxalate disease with high urinary oxalate. Taking normal dietary calcium with meals can reduce bowel absorption of oxalate. Animal protein and sugar High intake of some animal proteins can increase acid load, urinary calcium and uric acid while reducing citrate. Sugar sweetened drinks can add excess fructose and energy intake. Some carbonated drinks also contain acids or sugars that may be unhelpful. This does not mean that all protein or every occasional sweet drink causes stones. A balanced pattern is more sustainable than a rigid list of forbidden foods. Bowel disease and bariatric surgery Crohn's disease, bowel resection, pancreatic disease and some bariatric operations can increase oxalate absorption. When fat is not absorbed normally, it binds calcium within the bowel. More free oxalate is then available for absorption and urinary excretion. Chronic diarrhoea also reduces urine volume and citrate and can make urine acidic. These high risk situations often need specialist dietary and metabolic management rather than standard advice alone. Primary hyperparathyroidism Parathyroid hormone regulates calcium. Excess hormone can raise blood calcium and increase urinary calcium. Kidney stones may be the first clue to primary hyperparathyroidism. NICE recommends measuring serum calcium in adults with renal or ureteric stones. A raised result requires confirmation and endocrine assessment rather than assuming that every calcium stone has a parathyroid cause. Distal renal tubular acidosis Distal renal tubular acidosis reduces the kidney's ability to acidify urine. Urine remains relatively alkaline while blood can become acidotic. Low urinary citrate and high urine pH favour calcium phosphate stones and nephrocalcinosis. The condition may be inherited or associated with autoimmune disease and medicines. Treatment addresses systemic acid balance and stone prevention under specialist care. Recurrent urinary infection Recurrent infection with urease producing bacteria can cause struvite stones. Examples include some Proteus, Klebsiella and other organisms, although organism patterns vary. Not every urinary infection causes a stone, and not every stone related infection is struvite. Urine culture, stone analysis and complete imaging guide treatment. Anatomical factors A horseshoe kidney, ureteric narrowing, calyceal diverticulum or obstruction at the kidney outlet can impair drainage. Urinary diversion, neurogenic bladder and vesicoureteric reflux can also change infection and stone risk. Anatomy affects whether fragments can pass after shockwave treatment. Some structural problems require correction alongside stone removal to reduce recurrence or obstruction. Stones can remain asymptomatic A stone lying within a kidney calyx may be found incidentally during imaging for another reason. It may remain stable, grow, move or cause infection later. The natural history is not completely predictable. Watchful waiting can be appropriate for selected asymptomatic stones after discussing size, location, growth and individual risk. A stone in a solitary kidney, recurrent infection or a high risk occupation can alter the decision. What causes renal colic Renal colic usually begins when a stone enters the ureter and obstructs urine flow. The ureter contracts around the stone, pressure rises above it and the collecting system stretches. Prostaglandins increase blood flow and pressure within the kidney, contributing to pain and nausea. The term colic reflects waves of worsening pain, but discomfort can remain severe between waves. The classic pain pattern Pain commonly begins in the loin or flank below the ribs and may move towards the lower abdomen or groin. It can radiate into the testicle, penis, labia or upper inner thigh according to the stone's position. The pain is often severe, comes in waves and makes it difficult to remain still. The pattern is suggestive but not diagnostic. Aortic, abdominal, gynaecological and spinal emergencies can produce similar pain. Pain can move as the stone travels A stone high in the ureter often causes flank or upper abdominal pain. As it moves lower, pain may shift towards the groin and urinary symptoms can become more prominent. Changing pain location does not prove that the stone has passed. Pain can temporarily stop even when obstruction remains, so follow up should confirm passage or clearance when advised. Nausea and vomiting Severe ureteric pain frequently activates autonomic pathways and causes nausea, sweating and vomiting. Vomiting also reduces hydration and may prevent oral pain relief from being absorbed. Repeated vomiting can cause acute kidney injury and electrolyte disturbance. Inability to keep fluids or medicines down is a reason for urgent reassessment rather than continuing unsupported home care. Blood in the urine A moving stone can irritate the urinary lining and cause microscopic or visible haematuria. The urine may look pink, red, tea coloured or normal despite blood on dipstick. The absence of haematuria does not exclude a stone. Visible blood should not be assumed to come from a stone without appropriate evaluation, particularly when it is painless, persists or occurs in someone at risk of urinary cancer. Urinary symptoms from a low stone A stone near the bladder can cause urgency, frequency, burning or the sensation that urine must be passed repeatedly. Pain may be felt at the tip of the penis or within the urethral area. These symptoms overlap with cystitis and other lower urinary disorders. Urine testing and imaging help distinguish irritation from infection or another cause. Infection symptoms change the urgency Fever, shivering, feeling systemically unwell or confusion with suspected stone disease raises concern about infection. A stone can obstruct infected urine and prevent antibiotics from reaching adequate source control. The combination of obstruction and infection is a urological emergency. Urgent decompression is required using a ureteric stent or nephrostomy, with immediate antibiotics and cultures. Pyelonephritis without obstruction Pyelonephritis is infection of the kidney tissue and can cause fever, flank pain, nausea and urinary symptoms. It may occur without a stone or obstruction. Imaging is particularly important when symptoms are severe, kidney function worsens or improvement is inadequate. An infected obstructed system is more dangerous than uncomplicated pyelonephritis because drainage is blocked. Anuria and bilateral obstruction Anuria means that almost no urine is produced or reaches the bladder. One obstructed ureter usually does not cause anuria when the other kidney functions normally. Anuria can occur with bilateral obstruction, obstruction of a solitary functioning kidney, severe kidney failure or a blocked bladder outlet. Stone related anuria requires emergency assessment and urgent drainage when obstruction is confirmed. Solitary kidney A person may have one functioning kidney because of birth, surgery, donation or severe disease in the other kidney. Obstruction of that kidney can threaten total kidney function quickly. Pain, reduced urine or infection in a solitary kidney warrants urgent assessment even when symptoms appear similar to a previous stone. The threshold for intervention and follow up is lower because there is no second functioning kidney to maintain filtration. Abdominal aortic aneurysm is the critical mimic A leaking or ruptured abdominal aortic aneurysm can cause sudden back, flank, abdominal or groin pain and can be mistaken for renal colic. NICE advises considering ruptured AAA in people with new abdominal or back pain, collapse or loss of consciousness. Risk is higher after age 60, with smoking, hypertension or a known aneurysm. A first episode of apparent renal colic in an older adult must not be accepted without assessing circulation and considering urgent aortic imaging. Features that raise concern about AAA Collapse, faintness, cold clammy skin, very low blood pressure and a pulsatile abdominal mass increase concern. The classic combination is not always present, and a stable blood pressure does not completely exclude a leak. Pain may radiate from loin to groin exactly like a stone. Call 999 for sudden severe abdominal or back pain with collapse, marked weakness or signs of shock. Ectopic pregnancy An ectopic pregnancy can cause one sided abdominal or pelvic pain and internal bleeding. Vaginal bleeding, shoulder tip pain, dizziness or fainting increases concern, but symptoms vary. A pregnancy test forms part of assessment when pregnancy is possible, regardless of reported contraception. A ruptured ectopic pregnancy is life threatening and requires emergency gynaecological care. Ovarian torsion Ovarian torsion occurs when an ovary twists around its supporting structures and loses blood supply. It usually causes sudden severe one sided pelvic or lower abdominal pain, often with nausea and vomiting. Pain can fluctuate if the ovary twists and untwists, which can resemble colic. Urgent gynaecological assessment is required because delayed surgery can lead to loss of ovarian tissue. Appendicitis and bowel disease Appendicitis can begin with central abdominal pain and move to the right lower abdomen. Nausea, loss of appetite and fever may occur, but early presentations vary. Diverticulitis, bowel obstruction, inflammatory bowel disease and perforation can also cause flank or abdominal pain. Localised guarding, abdominal distension, persistent tenderness or bowel symptoms require assessment beyond a urinary stone diagnosis. Testicular torsion A lower ureteric stone can refer pain into the testicle. Testicular torsion causes sudden severe scrotal pain and threatens the blood supply to the testis. Any acute testicular pain requires direct scrotal assessment rather than assuming that it is referred pain. Emergency surgery may be needed within hours to preserve the testis. Other important differentials Musculoskeletal back pain, shingles, pancreatitis, gallbladder disease and renal infarction can mimic stone pain. Aortic dissection, mesenteric ischaemia and splenic disease are less common but dangerous possibilities. Severe pain out of proportion to examination, neurological deficits or an unusual pattern should prompt reconsideration. Imaging is valuable because it can identify both stones and alternative diagnoses. The clinical assessment The clinician asks about onset, location, movement and severity of pain. Questions cover fever, urinary symptoms, visible blood, vomiting, urine output and previous stone composition. Pregnancy possibility, solitary kidney, kidney disease, anticoagulation, cancer, infection and aortic risk affect urgency. Medicine, diet, family and metabolic histories guide later prevention but should not delay assessment of an emergency. Examination Temperature, pulse, blood pressure, oxygen level and general appearance identify sepsis or shock. The abdomen is examined for tenderness, guarding, masses and a pulsatile aorta when appropriate. The clinician assesses the flanks and bladder and performs genital or pelvic examination when another emergency is possible. A person with renal colic is often restless, while peritonitis may make movement painful. This difference is not reliable enough to replace imaging. Urinalysis Urine dipstick testing checks for blood, white cells, nitrites, protein, glucose and urine pH. Blood supports urinary tract irritation but is not specific to stones. White cells and nitrites increase concern about infection. A urine culture is required when infection is possible. Urine pH can provide a clue to uric acid, infection or calcium phosphate stones but cannot identify composition reliably by itself. Blood tests Blood tests assess creatinine, electrolytes, full blood count and inflammatory markers when renal colic is suspected. Serum calcium is measured in adults with kidney or ureteric stones to screen for disorders such as primary hyperparathyroidism. Urate and bicarbonate may be useful according to the stone type and history. A pregnancy test is required before radiation based imaging when pregnancy is possible. Non contrast CT KUB Low dose non contrast CT of the kidneys, ureters and bladder is the preferred standard adult test and is often described as the imaging gold standard. NICE recommends offering it urgently, within 24 hours, to adults with suspected renal colic. CT identifies stone size, location, density, obstruction and relevant anatomy. It can also detect many alternative causes of acute abdominal or flank pain. Contrast is not usually needed to identify a stone and can obscure small calcifications during the initial stone study. CT does not make the clinical assessment unnecessary A CT result must be interpreted with symptoms, urine tests, kidney function and infection risk. A small non obstructing kidney stone may be incidental and may not explain severe abdominal pain. A stone can coexist with appendicitis, infection, cancer or another condition. Severe sepsis or suspected ruptured AAA requires immediate emergency pathways rather than waiting routinely for a standard stone CT. Ultrasound Ultrasound can show hydronephrosis, some kidney stones, bladder retention and features of alternative urinary disease. It avoids ionising radiation but is less sensitive than CT for small ureteric stones. A normal ultrasound does not always exclude a stone or early obstruction. NICE recommends ultrasound instead of CT as first line imaging during pregnancy and for children and young people. Imaging during pregnancy Ultrasound is the first line test for suspected renal colic in pregnancy. Pregnancy itself can cause physiological dilatation of the urinary tract, making interpretation difficult. MRI without gadolinium may help define obstruction when ultrasound is inconclusive in specialist care. Radiation based imaging is considered only after a careful risk benefit assessment when the diagnosis remains important and other tests are insufficient. Plain abdominal X ray A plain kidney ureter bladder X ray can show many calcium and struvite stones. Uric acid stones are usually radiolucent, while cystine stones can be only faintly visible. Plain X ray is less sensitive than CT and does not reliably exclude obstruction or alternative abdominal disease. It can be useful for monitoring a known radiopaque stone or planning shockwave treatment. Confirming whether a stone has passed Catching a stone provides direct evidence of passage and allows laboratory analysis. Some services advise filtering urine through a clean stone strainer during conservative management. Pain stopping does not always prove passage. Follow up imaging may be needed when the stone was not retrieved, symptoms persist or kidney function was affected. A retained silent obstruction can damage kidney function despite temporary symptom improvement. Stone analysis NICE advises considering stone analysis for adults with renal or ureteric stones. The European Association of Urology recommends analysis in first time stone formers when material is available. Modern analysis uses methods such as infrared spectroscopy or X ray diffraction rather than appearance alone. Composition guides targeted prevention and can reveal infection, cystinuria, uric acid disease or a rare inherited disorder. Immediate pain management NICE recommends an NSAID by a suitable route as first line treatment for suspected renal colic. NSAIDs reduce prostaglandin activity, ureteric pressure and inflammation and often control pain better than opioids. They are not suitable for everyone. Acute kidney injury, significant CKD, previous ulcer bleeding, anticoagulation, allergy, pregnancy and cardiovascular disease can change the choice. The medicine and route should be selected by a clinician according to the person's risks. Paracetamol and opioids NICE recommends intravenous paracetamol when NSAIDs are contraindicated or do not provide enough relief. An opioid can be considered when both NSAIDs and intravenous paracetamol are unsuitable or insufficient. Opioids can cause sedation, nausea, constipation and respiratory depression and may worsen vomiting. Antispasmodic medicines are not recommended for suspected renal colic. Anti sickness treatment An antiemetic can reduce nausea and help you retain oral fluid and medicine. The choice depends on pregnancy, heart rhythm, other medicines and the degree of vomiting. Persistent vomiting despite treatment is a reason for hospital reassessment. Vomiting with infection, low blood pressure or reduced urine can indicate sepsis, obstruction or acute kidney injury. Fluid management during an acute attack Dehydration should be corrected carefully with oral or intravenous fluid according to severity. Forcing very large fluid volumes does not reliably push an obstructing stone through and can increase pressure and pain above the obstruction. Drink normally if you can, replacing ordinary losses without making yourself sick through excessive intake. People with heart failure, advanced kidney disease or fluid restrictions need individual advice. Conservative management Observation is appropriate when a ureteric stone is likely to pass, pain is controlled and there is no infection or threatened kidney function. The plan includes analgesia, anti sickness treatment, safety netting and follow up. The stone's size and location strongly affect the probability of passage. Conservative management must stop if infection, refractory pain, persistent obstruction or deteriorating kidney function develops. Which stones are more likely to pass Smaller and more distal ureteric stones are more likely to pass without a procedure. European guideline data suggest that about three quarters of ureteric stones smaller than 5 millimetres pass spontaneously, although results vary. A distal stone under 5 millimetres has a higher passage probability than a similar stone near the kidney. Size estimates and percentages cannot predict an individual outcome with certainty. Passage takes time A stone may pass within days, but the process can take several weeks. Pain can recur as the ureter contracts and the stone moves. Ongoing review checks symptom control, urine output and whether the stone has actually cleared. NICE recommends treatment within 48 hours for adults when pain remains intolerable despite adequate analgesia or the stone is unlikely to pass. Medical expulsive therapy Alpha blockers relax smooth muscle within the lower ureter and may improve passage in selected people. NICE advises considering an alpha blocker for a distal ureteric stone smaller than 10 millimetres. European guidance suggests that the greatest benefit is likely for distal stones between 5 and 10 millimetres. The treatment is used only when active removal is not immediately required and must stop if infection, uncontrolled pain or kidney deterioration develops. Alpha blocker safety Tamsulosin and related medicines can cause dizziness, postural hypotension, headache and ejaculation changes. Falls risk matters, particularly in older people and those taking other blood pressure medicines. Tell an eye surgeon about current or previous tamsulosin use before cataract surgery because it can affect the iris during the operation. This use may be off label and should be explained during prescribing. Medical expulsive therapy does not guarantee passage and does not replace follow up. When active stone treatment is needed Intervention is needed when a stone has a low likelihood of passing, causes persistent obstruction or produces pain despite adequate medicine. Kidney impairment, bilateral obstruction and obstruction of a solitary kidney are strong reasons for active treatment. Infection behind an obstruction requires immediate drainage before definitive stone removal. Stone growth, recurrent infection, occupational risk and personal preference also influence treatment of kidney stones. Infected obstruction is a urological emergency An obstructed collecting system containing infected urine can progress rapidly to sepsis and shock. Antibiotics begin immediately, but they are not enough without source control. The kidney is urgently decompressed using a ureteric stent or a percutaneous nephrostomy. Definitive stone fragmentation or removal is usually delayed until sepsis has resolved and antimicrobial treatment has been completed. Ureteric stent for emergency drainage A ureteric stent is a thin internal tube passed from the bladder through the ureter into the kidney. It allows infected or obstructed urine to drain around the stone. The stent does not necessarily remove the stone. A later procedure is often required. Stents can cause frequency, urgency, flank discomfort and blood in the urine and must not be forgotten after discharge. Percutaneous nephrostomy A nephrostomy is a tube placed through the skin directly into the kidney collecting system. It drains urine into an external bag and can rapidly relieve an infected or severe upper tract obstruction. Stenting and nephrostomy are both effective emergency drainage methods. The choice depends on anatomy, illness severity, expertise and practical considerations. The tube requires care and a plan for definitive treatment or removal. Shockwave lithotripsy Shockwave lithotripsy, shortened to SWL, uses focused energy from outside the body to fragment a stone. The fragments then pass through the urinary tract. It avoids insertion of a telescope into the ureter and usually has lower immediate morbidity than ureteroscopy. Several sessions may be needed, and success depends on stone size, location, density, body habitus and urinary anatomy. When SWL is used NICE recommends SWL for many renal stones smaller than 10 millimetres and ureteric stones smaller than 10 millimetres when suitable. It can also be considered for some stones between 10 and 20 millimetres. Very hard stones, lower pole kidney stones, obesity, long skin to stone distance and unfavourable anatomy can reduce success. Pregnancy, untreated infection and some bleeding risks are contraindications. Ureteroscopy Ureteroscopy passes a thin telescope through the urethra and bladder into the ureter or kidney. The surgeon can remove a small stone or fragment it with a laser and retrieve pieces with a basket. Ureteroscopy is more likely than SWL to produce stone free status after one procedure but has a higher procedure related complication rate. A temporary ureteric stent may be needed, although NICE advises that routine stenting is unnecessary after uncomplicated ureteroscopy for many stones under 20 millimetres. When ureteroscopy is preferred NICE recommends ureteroscopy for many ureteric stones between 10 and 20 millimetres. It is considered when SWL cannot target the stone, has failed or is unlikely to clear it promptly. It can be useful for hard stones, obesity, bleeding management constraints and anatomy unfavourable for SWL. Risks include infection, ureteric injury, bleeding, stent symptoms and the need for another procedure. Percutaneous nephrolithotomy Percutaneous nephrolithotomy, shortened to PCNL, removes a kidney stone through a small tract created from the skin into the kidney. A telescope and fragmentation equipment clear a larger stone burden more directly than SWL. NICE recommends PCNL for renal stones larger than 20 millimetres, including staghorn stones. It has a higher bleeding and organ injury risk than less invasive methods but offers the best chance of clearing large or complex stones efficiently. Staghorn stones A staghorn stone branches through the kidney collecting system. Many are infection related, although other compositions can form a staghorn shape. They can cause recurrent infection, progressive kidney damage and sepsis even when pain is limited. PCNL, sometimes through more than one access tract or staged with another method, is commonly required for complete clearance. Open or laparoscopic surgery Modern endoscopic and percutaneous techniques treat most stones. Open, laparoscopic or robotic surgery is now reserved for unusual large stones, complex anatomy or cases requiring reconstructive surgery at the same time. The approach is decided by a specialist stone team. The least invasive method is not automatically the best if it is unlikely to clear the stone or would require many repeated procedures. After a procedure Temporary blood in the urine, discomfort and urinary frequency can occur after stone treatment. A stent or nephrostomy requires clear instructions about care and removal. Fever, worsening pain, inability to pass urine or feeling systemically unwell after a procedure requires urgent assessment. Follow up imaging confirms whether the stone and clinically important fragments have cleared. Prevention begins with stone type and risk Everyone benefits from general hydration and dietary advice, but additional investigation depends on recurrence risk. Early onset, repeated stones, bilateral stones, a solitary kidney, infection stones and cystine or uric acid stones indicate higher risk. Bowel disease, bariatric surgery, nephrocalcinosis, CKD and a strong family history also justify more detailed assessment. A personalised plan is more accurate than giving identical restrictions to every stone former. Hydration is the cornerstone of prevention NICE advises adults with stones to drink 2.5 to 3 litres of water daily unless a fluid restriction applies. The practical aim is a consistently dilute urine rather than drinking the entire amount at once. More may be needed during hot weather or exercise, while less may be safe in heart failure or advanced kidney disease. Water is the main drink. Tea and coffee can contribute, while frequent sugar sweetened or carbonated drinks are less helpful. Citrate and lemon juice Citrate binds calcium and inhibits crystal growth. It also raises urine pH. NICE advises adding fresh lemon juice to water as part of recurrence prevention. Dietary citrate cannot replace prescribed potassium citrate when a specific metabolic abnormality requires treatment. People with kidney disease, high potassium or interacting medicines need clinical advice before potassium containing supplements. Maintain normal dietary calcium Do not remove calcium rich foods solely because a stone contains calcium. Normal dietary calcium helps bind oxalate in the bowel and supports bone health. A very low calcium intake can increase oxalate absorption and may worsen osteoporosis risk. Supplement decisions should consider meals, bone health, urine calcium and the reason for supplementation. Reduce excess salt Lower sodium intake reduces urinary calcium in many calcium stone formers. It also supports blood pressure control and improves the effectiveness of thiazide treatment. The adult target is no more than 6 grams of salt daily. Food labels and cooking patterns are often more important than removing the salt shaker alone. Stone specific prevention Potassium citrate can increase urine citrate and alkalinity and is used for recurrent calcium oxalate stones in selected adults. It is central to uric acid stone dissolution and prevention when urine is too acidic. Thiazide medicines can reduce urinary calcium in recurrent calcium oxalate stone formers with hypercalciuria after sodium restriction. Allopurinol or other treatment may be used when uric acid metabolism contributes, while cystinuria requires specialist high fluid and alkalinisation strategies. Uric acid stone dissolution Pure uric acid stones can sometimes dissolve when urine pH is raised with potassium citrate or sodium bicarbonate. Treatment requires urine pH monitoring because inadequate alkalinisation will not dissolve the stone and excessive alkalinity can encourage calcium phosphate crystallisation. An obstructed infected system still requires drainage. Dissolution treatment is not an emergency substitute. The stone composition and follow up imaging must be sufficiently certain before relying on chemolysis. Prevention of infection stones The priority is complete removal of infection stone material where possible and eradication or control of the associated infection. Residual fragments can act as a focus for rapid regrowth. Urine cultures and anatomical assessment help identify persistent infection or impaired drainage. Long term antibiotics are not a substitute for appropriate stone clearance, although selected people require specialist suppressive treatment. Metabolic evaluation A detailed evaluation may include blood calcium, creatinine, bicarbonate and urate together with one or two 24 hour urine collections. Urine testing can measure volume, calcium, oxalate, citrate, uric acid, sodium, pH and cystine when indicated. Results should reflect the person's usual diet and fluid intake unless the service gives different instructions. A single abnormal value is interpreted with stone composition, kidney function, medicines and collection quality. Who needs detailed metabolic testing Recurrent stone formers and people with bilateral stones, nephrocalcinosis, a solitary kidney or strong family history commonly need detailed assessment. Children, young adults and people with cystine, uric acid, infection or unusual stones also warrant specialist evaluation. Malabsorption, bariatric surgery, renal tubular acidosis and primary hyperparathyroidism create specific pathways. A first uncomplicated calcium stone still requires basic assessment, prevention advice and stone analysis when available. Prognosis Most small uncomplicated ureteric stones pass or are cleared without permanent kidney damage. The outlook changes when obstruction is prolonged, infection develops or stones recur repeatedly. A severe infected obstruction can cause sepsis and acute kidney injury within a short time. Long term prevention and confirmation of clearance reduce the risk of recurrence and silent damage. Living after a stone episode Keep a record of the stone size, location, composition and any procedure performed. Know whether a stent or nephrostomy remains and the date planned for removal. Maintain the agreed fluid and dietary plan and complete follow up imaging or metabolic tests. Seek reassessment for fever, worsening pain, reduced urine or recurrent blood rather than assuming every episode is an uncomplicated repeat stone. The main safety message Renal colic is a symptom pattern, not a complete diagnosis. Urgent imaging confirms the stone and helps exclude dangerous alternatives such as ruptured AAA, ectopic pregnancy and other abdominal emergencies. A stone with infection, anuria, a solitary obstructed kidney or uncontrolled symptoms requires urgent urological care. After the acute episode, hydration, stone analysis and risk based metabolic assessment help prevent recurrence.

Kidney stones range from silent kidney deposits to obstructing ureteric emergencies. Safe care confirms the diagnosis, excludes dangerous mimics, drains any infected obstruction promptly and uses stone size, location and composition to guide passage, intervention and prevention.