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.