Renal Stone Disease

and Christopher Isles²

(1)

Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK

(2)

Dumfries and Galloway Royal Infirmary, Dumfries, UK

Q1 What are urinary stones and how commonly do they occur?

Urinary stones (calculi) are abnormal crystalized aggregates of common dietary minerals normally present in the urine. Calcium (as calcium oxalate or calcium phosphate) stones are by far the most common with urate, struvite and cystine calculi being less common. Lifetime risk is about 12 % in men and 6 % in women. The risk of recurrence with calcium stones is around 35–40 % at 5 years and 50 % at 10 years.

Box 32.1 Frequency of Urinary Stones

Composition	Frequency (%)
Calcium oxalate	60
Calcium phosphate	20
Magnesium ammonium phosphate (struvite)	5–10
Uric acid	5–10
Cystine	1

We devote the discussion that follows to stones that form in the kidney as opposed to stones that form in the ureter or bladder

Q2 How do urinary stones form?

The pathophysiology of renal stones varies, depending on the stone composition. Stones form when there is an excess of a particular substance, dehydration or an environment that is otherwise favourable to stone formation, as shown in Box 32.2.

Box 32.2 Pathophysiology and Stone Composition

Pathophysiology	Stone composition
“Supersaturation” of otherwise soluble material	Calcium, oxalate, phosphate, urate
Low urinary pH (acid urine)	Urate
Chronic/recurrent infections of upper urinary tract with urease producing bacteria	Struvite
Inherited defect of tubular resorption	Cystine

Q3 What medical diagnoses may be associated with stone formation?

Many systemic conditions can predispose patients to urinary stone disease. Prolonged hypercalcaemia of any cause (hyperparathyroidism, sarcoidosis, excessive dietary/prescribed calcium) results in larger than normal levels of excreted urinary calcium. Calcium oxalate stones may occur with any chronic diarrhea illness e.g. Crohn’s disease. Calcium phosphate stones are associated with renal tubular acidosis, and urate stones with gout. Patients with recurrent/chronic urease producing bacterial infections of the upper urinary tract are at risk of struvite stones.