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Method-dependent differences in apparent sodium concentrations in plasma after exchange transfusions with citrated
J Schots1, H De Raeve, A Boeyckens
1Department of Clinical Chemistry, Academisch Ziekenhuis, Vrije Universiteit Brussel, Belgium.
Clinical Chemistry
|April 1, 1992
Summary
Citrate-dextrose-phosphate (CDP) blood transfusions paradoxically lowered plasma sodium levels detected by potentiometric methods. Flame photometry provided more accurate sodium measurements post-transfusion.
Area of Science:
- Clinical Chemistry
- Blood Transfusion Medicine
- Analytical Chemistry
Background:
- Accurate plasma sodium measurement is critical for patient management.
- Citrate-based anticoagulants are widely used in blood products.
- Discrepancies in sodium measurements have been observed with certain analytical methods.
Purpose of the Study:
- To investigate the cause of paradoxical low plasma sodium readings after exchange transfusions with citrate-dextrose-phosphate (CDP)-treated blood.
- To compare sodium measurements obtained by potentiometric methods versus flame photometry.
- To assess the impact of CDP and its components on sodium determination.
Main Methods:
- Exchange transfusions using CDP-treated blood and regular blood.
- In vitro addition of CDP solution, trisodium citrate, and Na2HPO4 to plasma pools.
- Sodium concentration determination using Ektachem 700 XR (potentiometric) and flame photometry.
- Analysis of analytical recovery of sodium added as CDP and NaCl.
Main Results:
- Plasma sodium levels were significantly lower (3-10 mmol/L) by Ektachem 700 XR after CDP-treated blood transfusions compared to flame photometry.
- Similar discrepancies were observed in vitro when adding CDP, trisodium citrate, or Na2HPO4 to plasma.
- Analytical recovery of sodium added as CDP was significantly lower by potentiometric methods than by flame photometry.
- Sodium recovery was also lower for sodium added as CDP compared to NaCl in potentiometric methods.
Conclusions:
- Potentiometric methods may underestimate plasma sodium concentrations following CDP-treated blood transfusions.
- The interaction between sodium ions and citrate/phosphate ions likely causes these analytical interferences.
- Flame photometry appears to be a more reliable method for sodium measurement in this clinical context.