Kidney stones

Introduction

Kidney stones affect up to 5% of the population, with a lifetime risk of passing a kidney stone of about 8-10%.1 Increased incidence of kidney stones in the industrialised world is associated with improved standards of living and is strongly associated with race or ethnicity and region of residence.2 A seasonal variation is also seen, with high urinary calcium oxalate saturation in men during summer and in women during early winter.3 Stones form twice as often in men as women. The peak age in men is 30 years; women have a bimodal age distribution, with peaks at 35 and 55 years. Once a kidney stone forms, the probability that a second stone will form within five to seven years is approximately 50%.1

Sources and search criteria

I searched Medline to identify recent articles (1990-2003) related to the evaluation and management of kidney stones. Key words used included kidney stones, urinary calculi, urolithiasis, urinary tract stones, and nephrolithiasis.

Classification and pathophysiology

Kidney stones are broadly categorised into calcareous (calcium containing) stones, which are radio-opaque, and non-calcareous stones. On the basis of their composition, stones are classified as shown in the table. The figure shows multiple calcium oxalate stones.

Multiple calcium oxalate stones (0.5 x 0.5 cm) in the collecting system of a kidney (reproduced courtesy of C F Verkoelen, Josephine Nefkens Institute, Netherlands)

Recent evidence indicates that formation of kidney stones is a result of a nanobacterial disease akin to Helicobacter pylori infection and peptic ulcer disease.4 Nanobacteria are small intracellular bacteria that form a calcium phosphate shell (an apatite nucleus) and are present in the central nidus of most (97%) kidney stones and in mineral plaques (Randall's plaques) in the renal papilla. Further crystallisation and growth of stone are influenced by endogenous and dietary factors. Urine volume, …