Free or unbound to serum protein (mainly albumin) type of calcium is called ionised calcium. Levels of ionized calcium provides insight on signs of kidney disease, parathyroid disease, and certain conditions that alter levels of albumin. However, total calcium remains the first line test for evaluation of calcium abnormality.
Calcium is the only mineral that has its own regulatory system (the parathyroid glands). Parathyroid glands control how much calcium is in our bones, and how much calcium is in our blood. A 6 hour fast is required for this blood test. However, drink plenty of water and take medications as prescribed.