Calcium Homeostasis: Plasma Calcium

Alkalosis

When alkalosis develops, hydrogen ions (H⁺) dissociate from albumin to buffer plasma pH. In exchange, Ca²⁺ is then bound to albumin. Calcium complexes also increase in the plasma.

The net result is serum ionised Ca²⁺ falls. This may be sufficient to produce signs and symptoms of hypocalcaemia.

Acidosis

When acidosis develops, H⁺ ions bind with albumin to buffer plasma pH. In exchange, Ca²⁺ is then released.

The net result is serum ionised Ca²⁺ rises.

Myeloma

In myeloma, massively increased levels of γ globulins can increase total plasma calcium, similarly, by binding.

Learning Bite: In alkalosis serum ionised Ca²⁺ falls but total calcium in serum is unchanged.

Learning Bite: Venous stasis during sampling is a cause of apparent hyperproteinaemia and increases calcium levels – do not use a tourniquet.