Kidney Stones
Nephrolithiasis — causes, symptoms and prevention
Kidney stones (nephrolithiasis) affect around 1 in 10 people in the UK and are a leading cause of emergency hospital admissions. Renal colic — the pain caused by a stone moving through the ureter — is one of the most severe pains known. Most stones pass spontaneously, but recurrence is common without preventive measures.
What are Kidney Stones?
Kidney stones are hard deposits of minerals and salts that form inside the kidneys when urine becomes supersaturated with certain substances. Calcium oxalate stones are the most common type, accounting for around 80% of all stones. Other types include uric acid stones (10–15%), struvite stones (associated with recurrent urinary tract infections), and cystine stones (rare, genetic). Stones range in size from a grain of sand to several centimetres. Small stones (<5mm) often pass spontaneously; larger stones (>10mm) usually require intervention. Risk factors include inadequate fluid intake, high animal protein diet, high salt intake, obesity, certain medications (topiramate, loop diuretics, antacids), and medical conditions including gout, hyperparathyroidism, recurrent UTIs, and inflammatory bowel disease (oxalate absorption).
Types & Causes
Calcium oxalate and calcium phosphate stones form when urinary calcium is high (hypercalciuria — from excess dietary calcium absorption, hyperparathyroidism, or vitamin D excess) or when urinary oxalate is elevated (high dietary oxalate — spinach, rhubarb, nuts — or fat malabsorption in IBD). Low urinary citrate (a natural stone inhibitor) also predisposes to calcium stones. Uric acid stones form when urinary pH is persistently low (<5.5) and uric acid is elevated — associated with gout, high-purine diet, and dehydration. Struvite (infection) stones form in the presence of urease-producing bacteria (Proteus, Klebsiella) that alkalinise urine — these can grow into large 'staghorn' calculi filling the renal pelvis. Cystine stones result from an inherited defect in cystine transport causing excessive urinary cystine excretion.
Signs & Diagnosis
Renal colic presents as severe, colicky flank pain radiating to the groin, loin-to-groin distribution, often with haematuria (visible or microscopic), nausea, vomiting, and an inability to find a comfortable position. Unlike peritonitis, patients with renal colic are typically restless rather than still. Fever suggests concurrent infection — an obstructing infected stone is a urological emergency requiring immediate drainage. Investigations: urine dipstick (haematuria present in 85%), urine culture (exclude infection), serum creatinine, calcium, uric acid, FBC; non-contrast CT KUB (gold standard — identifies stone size, location, and degree of obstruction); renal ultrasound (used in pregnancy and children to avoid radiation); all passed stones should be sent for chemical analysis.
Prevention & Lifestyle
A comprehensive evaluation of stone type, metabolic risk factors, and dietary habits informs individualised prevention strategies. The most important intervention for all stone types is adequate fluid intake — 2.5 to 3 litres per day of predominantly water, aiming for pale urine throughout the day. Dietary sodium restriction reduces urinary calcium excretion. Reducing excessive animal protein intake (red meat, shellfish) lowers urinary calcium and uric acid. For calcium oxalate stones, reducing high-oxalate foods (spinach, rhubarb, nuts, chocolate) and ensuring adequate dietary calcium (do not restrict — binds oxalate in the gut) is important. For uric acid stones, a low-purine diet and urinary alkalinisation are key. A 24-hour urine collection for metabolic workup is recommended after a first stone to guide personalised prevention. Recurrence rate is approximately 50% at 10 years without preventive measures.