Kidney Stones: Causes, Symptoms and Treatment

Kidney Stones: Causes, Symptoms and Treatment

Kidney stones (urolithiasis or nephrolithiasis) are hard mineral and salt crystals that form within the urinary tract — the kidneys, ureters, bladder, or urethra. They affect approximately 10% of adults in developed countries over a lifetime, with recurrence rates of 50% within 5–10 years without preventive treatment. Kidney stones cause some of the most intense pain in medicine — renal colic from a stone passing through the ureter is frequently described as worse than labour.

Beyond the immediate episode, recurrent stone formers are at increased risk of chronic kidney disease, hypertension, and cardiovascular disease. However, the majority of stones are preventable with appropriate dietary and pharmacological measures.

How Kidney Stones Form

Urinary stones form when the concentration of stone-forming substances in the urine exceeds their solubility threshold — a process called supersaturation. Crystal nucleation begins, and if supersaturation persists and inhibitors of crystal growth (citrate, magnesium, Tamm-Horsfall protein) are insufficient, crystals aggregate into stones.

Key factors promoting stone formation:

• Low urine volume — dehydration concentrates all urinary solutes
• High urinary excretion of stone-forming ions (calcium, oxalate, uric acid, cystine)
• Low urinary citrate (citrate inhibits calcium crystal growth)
• Abnormal urinary pH (acidic urine promotes uric acid stones; alkaline urine promotes calcium phosphate and struvite stones)
• Anatomical abnormalities — stasis in horseshoe kidney, medullary sponge kidney, ureteropelvic junction obstruction

Stone Types

Calcium Oxalate (Most Common — 75–80%)

Calcium oxalate monohydrate (COM) or dihydrate (COD) stones are the most common. Calcium oxalate supersaturation depends on urinary calcium and oxalate concentrations. Risk factors:

• Hypercalciuria — the most common metabolic abnormality in stone formers: absorptive (excessive calcium absorption from gut), renal leak (kidney fails to reabsorb filtered calcium), or resorptive (hyperparathyroidism driving bone calcium release)
• Hyperoxaluria — primary (rare genetic enzyme deficiency), enteric (fat malabsorption in IBD/short bowel → increased colonic oxalate absorption → hyperoxaluria), or dietary (excessive spinach, nuts, rhubarb, chocolate)
• Hypocitraturia — reduced citrate (renal tubular acidosis, hypokalemia, high-meat diet)

Calcium Phosphate (5–10%)

Associated with renal tubular acidosis (alkaline urine promotes calcium phosphate precipitation), hyperparathyroidism, and distal tubular defects.

Uric Acid (5–10%)

Form in persistently acidic urine (usually pH <5.5). High urinary uric acid excretion (hyperuricosuria) may contribute but is not required. Associated with:

• Gout and hyperuricaemia
• High purine diet (red meat, shellfish, organ meats)
• Type 2 diabetes and metabolic syndrome (insulin resistance causes impaired ammonium excretion → acidic urine)
• Chronic diarrhoea (stool bicarbonate loss → acidic urine)

Uric acid stones are radiolucent — invisible on plain X-ray but visible on CT. Importantly, they can dissolve completely with urinary alkalinisation (potassium citrate tablets to raise urine pH to 6.5–7.0) — medical dissolution is possible without surgery.

Struvite (Infection Stones — 5–10%)

Composed of magnesium ammonium phosphate; form only in the presence of urease-producing bacteria (Proteus, Klebsiella, Pseudomonas) that hydrolyse urea to produce ammonia, alkalinising urine. Form rapidly, often growing to fill the renal collecting system (staghorn calculi). Associated with recurrent UTIs; treatment requires both stone removal and antibiotic sterilisation.

Cystine (1%)

Rare genetic disorder (cystinuria) causing excessive cystine excretion; forms highly recurrent stones; requires urinary alkalinisation and high fluid intake; often requires specialist management.

Symptoms

Renal Colic

The classic presentation when a stone enters the ureter:

• Severe flank pain — sudden onset colicky (comes in waves) pain in the loin (between ribs and hip); may radiate to the groin, inner thigh, or genitalia as the stone descends
• Nausea and vomiting — severe, accompanying the pain
• Haematuria — blood in urine (macroscopic — visible; or microscopic); present in approximately 80–90% of ureteric stones
• Restlessness — patients cannot find a comfortable position (contrasts with peritonitis where the patient lies still)
• Dysuria and frequency — when the stone reaches the vesicoureteric junction (VUJ — junction of ureter and bladder)

Pain severity depends on degree of ureteric obstruction and rate of onset — a small stone causing complete acute obstruction may be more painful than a large stone with partial obstruction.

Large kidney stones within the renal pelvis may be asymptomatic ("silent stones") until they pass into the ureter.

Complications

• Obstructive uropathy — complete ureteric obstruction causes hydronephrosis (dilation of the kidney) and, if prolonged, irreversible kidney damage
• Infection + obstruction — infected hydronephrosis (pyonephrosis) is a urological emergency requiring urgent decompression (ureteric stent or nephrostomy) and IV antibiotics; can rapidly progress to urosepsis
• Chronic kidney disease — recurrent obstruction or bilateral disease

Diagnosis

Non-contrast CT KUB

Low-dose non-contrast CT is a standard initial investigation for adults with suspected renal colic; NICE recommends ultrasound first for pregnant patients and children. Non-contrast CT can detect common stone types (including calcium, uric acid, cystine and struvite), localise stones, measure size and density, and identify complications such as hydronephrosis. CT urography is a different, contrast-enhanced urinary-tract examination; the clinician chooses the appropriate protocol.

Ureteric stone size and location help estimate spontaneous passage; these estimates do not apply interchangeably to stones still within the kidney. The EAU guideline reports that approximately 75% of ureteric stones smaller than 5 mm passed spontaneously in the cited data. For stones smaller than 5 mm, reported passage was 89% in the distal ureter and 71% in the upper ureter. These are population estimates, not an individual prediction. Larger stones are less likely to pass, but treatment is not determined by a size threshold alone. Selected asymptomatic, non-obstructing renal stones may be monitored after discussing the risks and follow-up plan.

Ultrasound

Can detect renal stones and hydronephrosis; radiation-free; preferred in pregnancy and children; less sensitive for small ureteric stones.

Plain Abdominal X-ray (KUB)

Plain radiography can detect calcium-containing stones and may help follow known radiopaque stones, but sensitivity depends on size and other factors. Uric acid stones are radiolucent; cystine stones have poor radiopacity and may be faintly visible, so they should not be treated as invariably invisible.

Metabolic Stone Work-up

After the first recurrent stone or high-risk first stone (young patient, bilateral, large, or metabolic disease):

• 24-hour urine collection: calcium, oxalate, uric acid, citrate, creatinine, sodium, magnesium, phosphate, pH
• Serum: calcium, phosphate, urate, bicarbonate, creatinine, PTH (if hypercalcaemia)
• Stone analysis: if the stone is retrieved, chemical composition guides prevention

Treatment

Acute Management — Pain Relief

• NSAIDs (diclofenac, ketorolac IM/IV) — first-line analgesics; reduce prostaglandin-mediated ureteric spasm and oedema; superior analgesia to opioids for renal colic
• Opioids (morphine, pethidine) — for NSAID-contraindicated patients; IV in severe colic
• Antispasmodics (such as hyoscine) are not recommended by NICE for suspected renal colic; analgesia should follow the treating clinician’s assessment rather than assuming that an antispasmodic provides effective pain relief.
• IV fluids — for vomiting and dehydration; not shown to accelerate stone passage
• Alpha-blockers (such as tamsulosin) may be offered by the treating clinician as an off-label option for selected patients with distal ureteric stones measuring 5–10 mm who are suitable for conservative management. This is not a recommendation for all urinary stones, and the expected benefit varies.

Expectant Management (Watchful Waiting)

Observation may be appropriate for selected small ureteric stones when urgent removal is not indicated, with clinician-directed pain relief, follow-up and, in suitable cases, an alpha-blocker. Infection, pain that remains uncontrolled, persistent obstruction or worsening kidney function require prompt reassessment and may require intervention; a solitary kidney needs particular care. Maintain hydration according to clinical advice rather than forcing large fluid volumes during an obstructing episode. Long-term urine-output targets for preventing recurrence are different from acute treatment. The clinician sets the observation period; do not wait four weeks despite warning signs.

Shock Wave Lithotripsy (SWL / ESWL)

Non-invasive: focused acoustic shock waves generated externally, targeted at the stone under fluoroscopic or ultrasound guidance; fragment the stone into small pieces that pass spontaneously.

• Effective for stones ≤2 cm in the kidney or upper ureter
• Day-case procedure; conscious sedation or analgesia
• 70–80% stone-free rate at 3 months for 1–2 cm renal stones
• Requires a stone that can be reliably localised and an appropriate clinical setting; ultrasound can assist targeting, so radiopacity is not an absolute requirement. Renal function, obstruction distal to the stone and bleeding risk must be assessed.
• Contraindicated in pregnancy; less effective for hard stones (calcium oxalate monohydrate, cystine)

Ureteroscopy + Laser Lithotripsy (URS)

A thin flexible or semi-rigid ureteroscope is passed through the urethra → bladder → ureter to the stone. A holmium laser (or thulium fibre laser — most modern) fibre is passed through the scope and fragments the stone, with fragments retrieved or left to pass. The gold standard for ureteric stones and increasingly for renal stones <2 cm.

• 90% stone-free rate for ureteric stones; 80–90% for renal stones <2 cm

• Day-case or overnight procedure; general or spinal anaesthetic
• A ureteric stent may be placed for 1–2 weeks post-procedure to prevent ureteric oedema obstruction

Percutaneous Nephrolithotomy (PCNL)

For large renal stones (≥2 cm), staghorn calculi, or stones not suitable for URS/SWL. A percutaneous tract is created through the back into the kidney collecting system under fluoroscopic/ultrasound guidance; a nephroscope is passed and the stone is fragmented and removed.

• An established option for large or complex renal stones; complete clearance is not assured in one procedure, and residual stones may require additional treatment
• Minimally invasive PCNL (mini/ultra-mini PCNL) uses smaller tracts with equivalent efficacy and less bleeding
• 85–95% stone-free rate for large stones

Medical Stone Dissolution

Uric acid stones: urinary alkalinisation with potassium citrate, guided by individual urine-pH monitoring and clinical follow-up, may dissolve appropriately identified uric acid stones. Response and treatment duration vary; complete clearance and avoidance of surgical intervention are not guaranteed, and some patients need additional intervention.

Cystine stones: fluid intake and urinary alkalinisation are tailored to the patient. When indicated, tiopronin or D-penicillamine forms more soluble drug–cysteine complexes, reducing free cystine available for crystallisation; this is not primarily a reduction in total cystine excretion. These medicines require specialist supervision and monitoring.

Prevention

Dietary and pharmacological measures dramatically reduce recurrence:

For all stone types:

• High fluid intake — target urine output >2.5 litres/day; the single most important preventive measure; reduces recurrence by approximately 50%
• Dietary sodium restriction (<5 g NaCl/day) — excess sodium increases urinary calcium excretion
• Normal dietary calcium intake — paradoxically, low-calcium diets increase oxalate absorption; adequate calcium (1000–1200 mg/day from diet) binds gut oxalate

For calcium oxalate stones:

• Thiazide diuretics (hydrochlorothiazide, chlorthalidone) — reduce urinary calcium excretion; prescribed for hypercalciuria
• Potassium citrate — for hypocitraturia; increases citrate (crystal inhibitor) and alkalinises urine
• Reduce high-oxalate foods (spinach, rhubarb, nuts, chocolate) only if hyperoxaluria confirmed

For uric acid stones:

• Urinary alkalinisation (potassium citrate)
• Allopurinol — reduces uric acid production; may be used for hyperuricosuria after metabolic assessment. Recurrent uric acid stones alone do not automatically require allopurinol; a specialist selects treatment according to the findings, with urinary alkalinisation remaining central.

Urology and Kidney Stone Care in China

China's urology centres offer:

• Assessment and imaging: clinician-selected non-contrast CT or renal ultrasound, urine analysis, and metabolic work-up; contrast-enhanced CT urography is a different examination used when indicated
• Holmium and thulium laser ureteroscopy: flexible URS with modern laser platforms; high stone-free rates; day-case surgery
• Mini-PCNL: minimally invasive percutaneous surgery for large stones; experienced teams performing hundreds of procedures annually
• ESWL (shock wave lithotripsy): outpatient session
• 24-hour urine metabolic profiling: comprehensive prevention analysis
• Cost: care in China is generally less expensive than UK private treatment, but the hospital prices each case individually — ask us for the written quote before you commit.
• Full English care navigation from diagnosis through treatment and prevention planning

Contact a PriumCare care navigator to arrange a kidney stone assessment, imaging, or surgical treatment.

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Medical content based on MSD Manuals and international urolithiasis guidelines (EAU, AUA). Evidence reviewed 2025.

Targeted editorial source correction

Editorial source check: 25 October 2026. This update addresses the specific diagnostic and treatment claims documented below; it is not a whole-article medical review. The original publication date is retained.

• NICE NG118: imaging and renal-colic pain management
• ACR/RSNA: urography
• EAU: stone radiopacity and shock wave lithotripsy
• AUA: current management strategies for cystinuria

Targeted source clarification

Editorial source check: 25 October 2026. This update addresses the specific preparation, eligibility or care-planning statements above; it is not a whole-article medical review.

• Source 1
• Source 2

Targeted stone-treatment clarification

Editorial source check: 26 October 2026. This update checks only patient selection for alpha-blocker expulsive therapy and the limits of single-procedure PCNL clearance. It is not a whole-article medical review, adds no named clinical reviewer, and retains the original publication date.

• EAU Urolithiasis guideline: medical expulsive therapy, PCNL and residual stones

Targeted uric-acid stone clarification

Editorial source check: 26 October 2026. This update checks only whether hyperuricosuria is required for uric acid stones and the individual selection of allopurinol described above. It is not a whole-article medical review, adds no named clinical reviewer, and retains the original publication date.

• EAU Urolithiasis guideline: uric acid stone formation and recurrence prevention

Targeted editorial source check — 26 October 2026: only the uric-acid oral-chemolysis statement was reassessed against the EAU Urolithiasis guideline, section 3.4.4. Dissolution may be incomplete and further intervention may be needed; no fixed clearance deadline is promised. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.