The use of the hemolysis index as an indirect indicator of whole blood sample quality.

Objectives: The aim of this study is to assess the discrepancies between potassium values obtained from point-of-care testing and laboratory analyzers, and to propose a straightforward method to indirectly assess the likelihood of hemolysis in whole blood samples.

Methods: The data were collected from 409 hospitalized patients (199 males, 210 females; median age 78 years, interquartile range 55-87) in whom were simultaneously requested the blood gas profile, including electrolytes (Na, K, Cl and Ca) on the GEM Premier 5000 blood gas analyzer and K in plasma samples on the Cobas analytical system.

Results: The Wilcoxon test showed a significant difference (p<0.0001) for K measurements, with a number of positive differences between Cobas and GEM Premier 5,000 of 110 and negative differences of 293. The median value of the hemolysis index was 7 (95 % CI for the median 6 to 8). The differences between the two K measurements obtained from plasma and whole blood samples showed a lowest and highest differences of -1.7 and 4.6 mmol/L. The median difference was 0.63 (95 % CI for the median: 0.54-0.73) and the interquartile range (IQR) was 0.48-0.9. Overall, 89 samples (21 %) displayed a difference larger than the relative change value.

Conclusions: The presence of hemolysis in plasma samples should alert laboratory professionals to carefully evaluate the corresponding whole blood results. Concordant values indicate the presence of hemolysis in the whole blood sample, while discordant values suggest that hemolysis only affects one of the two samples.