Protein-Bound Calcium in Human Serum. Quantitative Examination of Binding and its Variables by a Molecular Binding Model and Clinical Chemical Implications for Measurement of Ionized Calcium

Abstract

Ultrafiltration and spectrophotometric methods have shown that protein binding of calcium (CaPr) in normal serum follows a simple mass law with an apparent maximum binding capacity of 0.12 mmol Ca/g protein, 90% being due to albumin. The effects of pH, temperature, and magnesium ions on CaPr have been quantitatively described by a previously suggested albumin-calcium binding model. CaPr was highly predictable in normo-, but not in dysproteinaemic subjects. The implications for interpretation of S-Ca values and the limited indications for (Ca⁺⁺) measurements have been discussed.

Key Words:

• Albumin
• calcium ions
• gammaglobulin
• hypercalcaemia
• hyper-parathyroidism
• paraprotein
• pH
• protein binding
• serum calcium
• serum protein
• temperature
• ultrafiltration