Which specimen is acceptable for the determination of total calcium?

Heparinized plasma is considered the most acceptable specimen for the determination of total calcium due to its ability to prevent coagulation without chelating calcium ions. Heparin, as an anticoagulant, allows for the maintenance of blood constituents, including calcium, in their soluble form.

Unlike other anticoagulants, EDTA and oxalate bind calcium ions, thereby affecting the measured levels of total calcium and potentially leading to falsely low results. Fluorinated plasma is less commonly used in clinical practice and may also contain fluoride ions that could interfere with calcium measurement. Thus, heparinized plasma preserves the integrity of calcium in the sample, ensuring accurate assessments for clinical purposes.