Abstract

Urinary calculi form when poorly soluble substances, such as calcium oxalate, cystine or uric acid, crystallise out from a supersaturated solution in urine. It should therefore be possible to prevent the formation of stones by lowering the concentration of the solute, by increasing the solubility of the solute, or by inhibiting crystal growth. The simplest way of reducing the concentration of any of the solutes is by producing a water diuresis and thus increasing the volume of solvent. Clear evidence that this is effective has been obtained only for cystine stones¹ and ‘hot weather’ stones,² but it is worth trying in all forms of urinary lithiasis. Because most other methods of preventing calculi are specific, it is important to identify the type of stone and diagnose its aetiology before starting therapy.