Idiopathic hypercalciuria

Idiopathic hypercalciuria is the presence of excess calcium in the urine without obvious cause.Severe dietary calcium restriction is inappropriate. Intake of milk, cheese, and white bread if this is fortified (as it is in the UK) with calcium and vitamin D is reduced. Vitamin D supplements should be avoided.

Dietary calcium restriction results in hyperabsorption of oxalate, and so foods containing large amounts of oxalate should also be limited. The advice of a dietitian is helpful. A high fluid intake should be advised as for idiopathic stone-formers.

Patients who live in a hard-water area may benefit from drinking softened water.

If hypercalciuria persists and stone formation continues, a thiazide is used (e.g. bendrofluazide 2.5 or 5 mg each morning). Thiazides reduce urinary calcium excretion by a direct effect on the renal tubule. They may precipitate diabetes mellitus or gout and worsen hypercholesterolaemia.

Avoidance of excessive sodium intake is also advisable as sodium and calcium excretion are linked.

Hypercalciuria can occur at any age, including newborns. The peak incidence of idiopathic hypercalciuria is in children aged 4-8 years. The age distribution of children with secondary hypercalciuria reflects that observed in the underlying etiology.