What percentage of serum calcium is ionized (Cai)?

The correct percentage of ionized serum calcium (Cai) is around 45%. This portion of serum calcium is the biologically active form, crucial for various physiological functions including muscle contraction, nerve transmission, and blood coagulation.

Understanding this percentage is important in clinical settings, as it helps in interpreting calcium levels in patients. The total serum calcium levels can be misleading without considering the ionized fraction, especially in conditions that affect protein levels, such as in cases of acidosis or alkalosis.

The remaining percentage represents calcium that is either bound to proteins (mostly albumin) or complexed with other molecules, and understanding the dynamic between these fractions is essential in diagnosing and treating disorders related to calcium metabolism. Thus, the knowledge of approximately 45% of serum calcium being ionized reflects an important concept in clinical biochemistry.