Kidney Stones (Urolithiasis) — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Kidney stones (urolithiasis, nephrolithiasis) are solid crystalline deposits that form in the renal collecting system when urine becomes supersaturated with stone-forming substances. They affect approximately 11% of men and 6% of women over their lifetime, with incidence rising globally in parallel with increasing obesity and diabetes. Recurrence is common — the 10-year recurrence rate is approximately 50% without preventive measures. Stone composition: calcium oxalate (most common — 70-80%), calcium phosphate (10%), uric acid (5-10% — increasing with obesity/gout), struvite/infection stones (5% — Proteus, Klebsiella UTI), and cystine (rare — inherited). Stones range from microcrystals to staghorn calculi filling the entire renal pelvis. Stone size, composition, location, and patient risk factors (anatomical abnormalities, metabolic disorders, family history) determine both acute management and long-term prevention strategy. Calcium oxalate monohydrate (Randall's plaque — apatite deposits on renal papilla) is the nidus for most calcium oxalate stone formation.

Kidney stones form when urine concentration of stone-forming salts exceeds their solubility threshold. Key risk factors: dehydration/low fluid intake (most important — reduces urinary volume, concentrating stone-forming salts), hot climate and high physical activity (increase insensible fluid loss), obesity (promotes hypercalciuria, hyperuricosuria, hypocitraturia), type 2 diabetes and metabolic syndrome (uric acid stones), diet high in animal protein, sodium, and oxalate-rich foods (spinach, nuts, chocolate), family history (10-30% increased risk), hyperparathyroidism (hypercalciuria), intestinal malabsorption (Crohn's disease, gastric bypass — oxalate hyperabsorption causing calcium oxalate stones), recurrent urinary tract infections (struvite stones), gout (uric acid stones), renal tubular acidosis (calcium phosphate stones), and certain medications (indinavir, topiramate, acetazolamide).

Renal colic is the classic presentation: sudden, severe, colicky (coming in waves) loin pain radiating from the flank to the groin and genitalia, following the course of the ureter. The pain is typically excruciating — patients are unable to find a comfortable position (in contrast to peritonitis where patients lie still). Associated nausea and vomiting (often severe), microscopic or macroscopic haematuria (blood in urine — present in 80-90%), and urinary frequency/urgency if the stone is at the vesicoureteric junction (VUJ). Low-grade fever from associated inflammation. Large renal calculi (staghorn stones) may be completely asymptomatic and discovered incidentally on imaging. Ureteric obstruction with superimposed infection (obstructed infected kidney) is a urological emergency presenting with sepsis and obstructed pyrexia — requires urgent decompression.

CT KUB (non-contrast CT of kidneys, ureters, and bladder) is the gold standard first-line investigation — sensitivity 97%, specificity 96%; identifies stone size, density (Hounsfield units), and location; detects hydroureter and hydronephrosis; identifies alternative diagnoses (aortic aneurysm, appendicitis). Urine dipstick: haematuria (positive in 80-90%), nitrites and leucocytes (infection). Urine culture: mandatory in suspected or confirmed urinary tract infection. Ultrasound: first-line in pregnant women and children (avoids radiation); detects hydronephrosis but misses small ureteric stones. Plain abdominal X-ray (KUB): identifies radio-opaque stones (calcium, struvite) — not sensitive enough alone. Blood tests: FBC, U&E (renal function), calcium (hyperparathyroidism), uric acid, bicarbonate (RTA). Stone analysis (after passage or surgical retrieval): guides metabolic evaluation and preventive strategy. 24-hour urine collection in recurrent stone formers: measures volume, calcium, oxalate, uric acid, citrate, sodium — guides targeted prevention.

Pain management (renal colic): NSAIDs (diclofenac IM/PR, ketorolac IV) are first-line — more effective than opioids for ureteric colic and reduce stone-related oedema. Opioids (morphine, oxycodone) if NSAIDs contraindicated. IV or oral hydration. Anti-emetics for nausea. Watchful waiting with medical expulsive therapy: ureteric stones under 5mm — 95% pass spontaneously (mean 4 weeks). Stones 5-10mm — 50% pass with medical expulsive therapy: tamsulosin 0.4mg daily (alpha-1 blocker relaxes ureteric smooth muscle, accelerating stone passage). Stones over 10mm or those causing persistent obstruction, infection, or intractable pain require intervention. Extracorporeal Shock Wave Lithotripsy (ESWL): high-frequency shock waves break stones under 2cm into passable fragments — non-invasive, outpatient. Ureteroscopy (URS) + laser lithotripsy (holmium laser): endoscopic approach via urethra — treats ureteric stones of any size; increasingly preferred over ESWL for UVJ stones. Percutaneous Nephrolithotomy (PCNL): minimally invasive keyhole renal access — for large renal stones (over 2cm) or staghorn calculi. Uric acid stones: alkalinisation of urine with potassium citrate (pH 6.5-7.0) can dissolve uric acid stones without surgery. Infected obstructed kidney: emergency ureteric stenting or percutaneous nephrostomy for drainage, then definitive stone treatment after infection treated.

Obstructive uropathy from an untreated impacted ureteric stone causes progressive hydronephrosis and renal damage — bilateral ureteric obstruction or obstruction of a single kidney constitutes an emergency. Urosepsis is the most dangerous complication: an obstructed infected kidney (obstructive pyrexia) with bacteria trapped proximal to the stone carries mortality above 10% even with treatment, requiring emergency ureteric decompression by stenting or percutaneous nephrostomy before definitive stone clearance. Recurrent stone episodes are associated with cumulative CKD risk — each episode carries a 40-50% increased risk of reduced eGFR over time. Staghorn calculi (typically struvite infection stones filling the renal pelvis and calyces) cause progressive chronic pyelonephritis, cortical scarring, and eventual renal failure if untreated, as well as severe life-threatening urosepsis. Acute kidney injury from prolonged bilateral obstruction may result in irreversible renal damage if not promptly decompressed. Stone disease also causes significant quality-of-life impairment, work absence, and healthcare utilisation.

High fluid intake is the single most effective prevention measure — target urine output above 2 litres per day (minimum 2.5L fluid intake daily), aiming for pale urine. Increase fluids in hot weather, with exercise, and after each stone episode. Dietary measures: reduce sodium intake (under 2300mg/day — reduces hypercalciuria), reduce animal protein (under 80g/day), maintain normal calcium intake (800-1200mg/day from diet — do NOT restrict dietary calcium, which paradoxically increases oxalate absorption). Reduce high-oxalate foods (spinach, nuts, chocolate, rhubarb) in calcium oxalate stone formers. Achieve healthy weight and exercise regularly. Specific prevention for recurrent stone formers (based on 24-hour urine and stone analysis): potassium citrate for hypocitraturia and uric acid stones; hydrochlorothiazide for hypercalciuria; allopurinol for hyperuricosuria; pyridoxine (B6) for primary hyperoxaluria.

Seek emergency medical care immediately for: severe loin pain with fever and rigors (obstructed infected kidney — urosepsis requiring urgent drainage), complete inability to pass urine (anuria — bilateral ureteric obstruction or obstruction of a single kidney), known kidney stone with fever above 38°C, worsening pain despite maximum analgesia, or any stone-related emergency in a solitary kidney or transplant kidney. Go to the emergency department for first presentation of renal colic — require imaging to confirm diagnosis, assess stone size, and exclude alternative diagnoses. See a urologist promptly for stones over 5mm that are not passing, recurrent kidney stones, any stone in a child, or stones associated with recurrent UTI.