Heparin interference in whole blood sodium measurements in a pediatric setting.

OBJECTIVES: In a pediatric setting, the incomplete filling of heparinized syringes is not an uncommon occurrence and has led to reports of falsely low hyponatremia in our institution. Little is known about heparin interference on sodium determination in whole blood, and our study aimed to investigate this interference due to excessive concentrations of heparin in pediatric specimens. DESIGN AND METHODS: Three different types of syringes were filled with various amounts of blood to mimic greater than normal concentrations of heparin. Specimens were analyzed on an ABL 725 blood gas analyzer, and corresponding plasma fractions were analyzed on a VITROS 950 chemistry system. In a separate study, paired patient samples consisting of a capillary tube and microtainer clot were similarly analyzed. RESULTS: The presence of lithium heparin at 100 units/mL in blood caused a significant negative bias of 2-3 mmol/L in sodium concentration with the ABL 725, but no significant bias occurred when the corresponding plasma fraction was analyzed on the VITROS 950. For syringes containing electrolyte-balanced heparin, a similar negative bias was observed for blood but was not significant. Capillary tubes contained high concentrations of heparin (>100 units/mL) even when completely filled. Sodium results from capillary samples averaged 3.4 mmol/L lower than the corresponding serum values. These effects were independent of the sodium concentration across a wide range. CONCLUSIONS: Small blood volumes collected with heparinized sampling devices in pediatric samples lead to excess heparin that may significantly affect sodium determinations and spur false reports of critical hyponatremia.

Challenges of implementing point-of-care testing (POCT) glucose meters in a pediatric acute care setting.

OBJECTIVES: To investigate factors contributing to analytical bias in POCT glucose values generated by the NICU versus the core laboratory. METHODS: The LifeScan Flexx hospital system glucose meters (SureStep) were used in precision and comparison studies between the NICU and laboratory (ABL715 and Vitros 950). RESULTS: Analysis of 40 neonatal blood samples revealed a positive bias between the NICU glucose meters versus either the laboratory glucose meter or instrument (mean difference of 0.28 and 0.21 mmol/L, respectively). Linear regression analysis (R2 = 0.0584) of the difference in glucose results versus time elapsed between measurements indicated that the bias observed between the NICU and laboratory glucose meters was not due to in vitro glycolysis for samples transported on ice. Further analysis indicated that the bias appeared to be mostly operator driven, with different NICU operators exhibiting different mean biases. Increasing the amount of blood applied to the SureStep Pro test strip (e.g., 60 vs. 20 microL), led to higher values for glucose concentration for the same blood. Nearly 50% of all glucose values reported for the NICU were obtained by the SureStep Flexx glucose meters in a 3-month period following the introduction of POCT, yet the number of laboratory-reported glucose results for the same period increased by 21% as compared to the previous year. CONCLUSIONS: Operator error appears to be a source of bias present between the NICU and laboratory, and despite glucose meter utilization in the NICU, the number of glucose measurements by the central laboratory increased after POCT introduction.