Special Precautions/Comments:

Unstable, send separate sample to laboratory urgently for analysis within 30 minutes.

Additional Information:

Ionised calcium is the biologically active form of calcium and is approximately 55% of total circulating calcium. The ionised calcium can be measured on a blood gas machine and is useful if the adjusted calcium results would be invalid or spurious, such as in hypoalbuminaemia or in acidosis.  

In acidaemia, high levels of H+ bind to albumin displacing calcium, causing a relative increase in ionised calcium. In alkalaemia, calcium binds to albumin causing a relative decrease in ionised calcium.