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Donnan effect or protein interference in ionised calcium measurements?
Annals of Clinical Biochemistry
|September 1, 1983
Summary
The ionized calcium concentration is higher in serum than ultrafiltrate due to the Donnan equilibrium. This difference is a predictable outcome and not caused by protein interference with calcium electrodes.
Area of Science:
- Biochemistry
- Physical Chemistry
Background:
- Ionized calcium is critical for physiological processes.
- Discrepancies in ionized calcium measurements between serum and ultrafiltrate exist.
- The role of protein interference versus equilibrium effects is debated.
Purpose of the Study:
- To investigate the cause of higher ionized calcium in serum compared to ultrafiltrate.
- To determine if the Donnan equilibrium or protein interference explains the observed difference.
Main Methods:
- Development of a theoretical model.
- Analysis of ion distribution across a semipermeable membrane.
Main Results:
- The theoretical model predicts a higher ionized calcium concentration in the serum sample.
- The observed difference is consistent with the principles of the Donnan equilibrium.
- Protein interference with calcium-specific electrodes was ruled out as the primary cause.
Conclusions:
- The Donnan equilibrium adequately explains the higher ionized calcium concentration in serum.
- The findings clarify measurement discrepancies and are not due to electrode artifacts.