Oral calcium-loading test in infancy, with particular reference to idiopathic hypercalcaemia.

An oral calcium-loading test suitable for infants is described and the usual response defined. In four acute cases of idiopathic hypercalcaemia a high and sustained rise in serum calcium occurred, suggestive of hyperabsorption and consistent with a vitamin-D-like effect. In four further infants with a milder illness suggestive of hypercalcaemia the fasting calcium levels were not grossly raised, but the test produced an exaggerated hypercalcaemic response. In this type of patient the test is more sensitive in the diagnosis of idiopathic hypercalcaemia than isolated measurements of serum calcium, especially if these are taken in the fasting state. Five patients on treatment and three whose treatment had been discontinued (but who subsequently relapsed or made a poor recovery) showed abnormal loading tests at a time when fasting calcium levels were normal. In two cases full recovery from the disease was associated with reversion of the test to normal. The test can therefore be used to indicate activity of the disease and consequently as a guide to therapy. In two cases a persistently abnormal loading test was associated with a poor long-term prognosis.