The metabolic basis for urolithiasis

Renal tract stones are common, more so in men, and among Asians and Caucasians, especially in warm climates. They are associated with a greater consumption of animal protein and refined foods, and decreased fluid intake. There are several types, most commonly consisting of calcium phosphates and oxalates; others are composed of magnesium ammonium phosphate (struvite), uric acid or cystine. Struvite stones are associated with urinary tract infections, often of urease-secreting bacteria that increase urinary ammonium concentration. Calcium stones may form for a number of reasons, including hypercalciuria and hyperoxaluria. Hypercalciuria may arise from changes to calcium resorption from bone, or renal and gastrointestinal tract handling of calcium; these are often associated with changes to parathyroid hormone secretion. Hyperoxaluria can arise from increased production or increased gut absorption. Other factors causing hypercalciuria include renal tubular acidosis or conditions that reduce the urinary concentrations of certain inhibitors, such as citrate and magnesium. Uric acid and cystine stones can form as a result of increased production or urinary concentration of the primary constituents. The assessment, investigation and management of patients with different types of stones is described.