Resolving Pseudohyponatremia: Validation of Plasma Sodium on Radiometer ABL800 Blood Gas Analyzers for Immediate Reflex Testing.

OBJECTIVE: To perform validation of plasma sodium on blood gas analyzers to reflexively correct erroneous measurements by ion-selective electrodes (ISEs). METHODS: We compared remnant specimens of whole blood and plasma collected by lithium heparin vacutainer with normal protein concentrations and no lipemia. Whole-blood specimens were tested for sodium concentration on the ABL800 Flex blood gas analyzer, followed by centrifugation for plasma separation, and repeat sodium determination on an aliquot of the plasma only. Also, plasma specimens were analyzed by indirect ISE on the Cobas 8000 series and by direct ISE on the ABL800 Flex for instrument comparison. RESULTS: Plasma aliquots yielded comparable results to the parent whole-blood specimen, with an average change of -1.33 mmol/L (R2 = 0.9727). Comparison of indirect ISE to direct ISE similarly yielded comparable results, with an average change of + 0.8 mmol/L (R2 = 0.9016). CONCLUSION: Plasma is a valid specimen matrix for use on blood gas analyzers for sodium determination, eliminating the need for re-collection of whole-blood specimens from patients with pseudohyponatremia.