Pseudohypercalcaemia in patients with heat cramps: implications on clinical practice.

Hypercalcaemia is often thought to provide important clues to the presence of unsuspected illness. A presumptive diagnosis of hypercalcaemia may often be made on an elevated total serum calcium concentration although it should, strictly speaking, refer to an elevation in the physiologically important ionized (free) calcium concentration. Pseudohypercalcaemia is rare, but should be excluded before pursuing unnecessary investigation for hypercalcaemia. Pseudohypercalcaemia refers to an increased serum total calcium concentration but in the presence of a normal ionized serum calcium level. Heat-related illness, although not widely reported, is an important cause of pseudohypercalcaemia. We describe three patients with heat cramps who were initially suspected to have hypercalcaemia.