B-142 Determining Hemolysis Index Cutoffs for Potassium Measurement in Pediatric Population on the VITROS XT 7600

Abstract Background Hemolysis, the breakdown of erythrocytes with release of intracellular components, is the most common preanalytical error, accounting for the majority of unsuitable specimens. Modern chemistry analyzers quantify hemolysis and assign a hemolysis index (HI) to samples. While manufacturers provide suggestive HI cutoffs for analytes susceptible to hemolytic interference, the evidence supporting these thresholds is often unclear. Potassium is one of the most affected analytes by hemolysis due to the 30-40-fold higher intracellular concentration, thereby resulting in pseudohyperkalemia and pseudoeukalemia. Few studies have investigated HI cutoffs for potassium measurement, and none have accounted for age-related differences. Given that hemolysis is more prevalent in the pediatric population, we aimed to establish appropriate HI cutoffs in the pediatric population. Methods Plasma potassium test results (N = 9,227) and their corresponding HI were extracted from two VITROS XT 7600 analyzers (QuidelOrtho) at McMaster Children’s Hospital. Data were explored based on sample type (capillary, venous, arterial, and central line) and age. Data were divided into two age groups: 2,788 infants (<1 year) and 6,418 older children (1 year up to 18 years). Analyses were done separately for each group. Each age group was further divided into bins based on the HI value. The bin with the lowest level of hemolysis (HI <15) was used as the base group for comparison. The relative difference in mean potassium (deltaK) between a bin and the base group was calculated. The maximum thresholds examined were: (1) 5% (allowable performance limit, Institute of Quality Management in Healthcare), and (2) 13.8%, the reference change value (RCV) calculated using the within-subject biological variation of 4.6% for a pediatric population (Clin Chem. 2014 Mar 1;60(3):518-529) and an analytical coefficient of variation of 0.8% from our instruments. Results Capillary samples had a higher median potassium value (5.37 mmol/L) and HI (78) compared to other sample types (3.84-4.02 mmol/L, HI: 0). Over 90% of capillary samples were drawn from infants (<1 year), who have a higher reference interval than older children. Regression analysis showed positive correlation between deltaK and HI in both age groups with best-fit equations deltaK=0.0112xHI for infants and deltaK=0.0051xHI for older children (HI =150), suggesting hemolytic interference is more severe in infants. The HI cutoffs corresponding to a 5% and 13.8% increase in potassium were 25 and 70 for infants and 50 and 140 for older children, respectively. Applying these thresholds would reduce the number of falsely elevated potassium results by 30% and 60% for infants, and 16% and 6% for older children. Conclusion We have shown that establishing HI cutoffs for the pediatric population requires separate thresholds for infants and older children. Implementing validated HI cutoffs is important for minimizing falsely elevated potassium results while reducing unnecessary specimen rejections. Although capillary sampling is widely used in infants, our findings highlight the need for improved blood collection techniques to ensure accurate potassium measurement. Venous sampling had a lower prevalence of hemolysis in infants and is therefore preferred method for accurate potassium measurement.