Interchangeability of Electrolyte and Metabolite Testing on Blood Gas and Core Laboratory Analyzers.

Background: Using blood gas (BG) analyzers as backups for core laboratory analyzers has the potential to greatly reduce turnaround times and costs.

Methods: One venous blood gas syringe, one plasma separator tube (PST), and one serum separator tube (SST) were drawn from 42 healthy individuals. All samples were run on the GEM4000 BG analyzer whereas the PST and SST samples were also run on the Roche Modular chemistry analyzer. Blood electrolyte and metabolite parameters were compared for paired measurements, and their differences were assessed for statistical and clinical significance.

Results: Whole blood on GEM4000 and plasma/serum on Roche Modular produced incomparable results for Na+ in plasma and serum (2.5 percentile difference, GEM4000 - Modular: -4.975 and -4.95 mmol/L, respectively) and K+ in serum (2.5 percentile difference, GEM4000 - Modular: -0.7975 mmol/L). When comparing whole blood to plasma/serum samples, all from the GEM4000, incomparable parameters were also found for Cl- in plasma and serum (97.5 percentile difference, plasma or serum - whole blood: 6 and 5 mmol/L, respectively), and K+ in serum (97.5 percentile difference, serum - whole blood: 0.7 mmol/L). None of the parameter differences when comparing plasma/serum results on the GEM4000 to those on the Roche Modular were found to be clinically significant.

Conclusions: The off-label use of plasma/serum on a BG analyzer produced electrolyte and metabolite measurements that were more interchangeable with standard core laboratory analyzer results than with its designated whole blood samples. The interchangeability of results, therefore, seems to be affected more by different sample types than by different measurement methods.