Relationship between free hemoglobin (hemolysis), potassium and ionized calcium in lithium heparin blood gas samples collected intraoperatively.

OBJECTIVE: Develop sample acceptability rules by determining the relationship between free hemoglobin level (hemolysis) and potassium or ionized calcium in blood gas samples collected intraoperatively. DESIGN AND METHODS: Hemolysis was assessed visually or by H index for lithium heparin blood gas samples collected intraoperatively. During periods one and three this was done using two different rules for visual assessment of centrifuged lithium heparin plasma. During period two H index was measured for all visually hemolyzed samples on a Roche Cobas c501 analyzer to determine acceptability. Potassium and ionized calcium were measured in 75 lithium heparin whole blood samples on a Radiometer ABL90 to correlate H index and potassium or ionized calcium. RESULTS: During period one 35 of 5808 (0.6%) blood gas samples had visual hemolysis levels exceeding tolerance for reporting of potassium. By switching to measured H index using a laboratory-established threshold, during period 2 we estimate that 171 of 5396 (3.2%) blood gas samples exceeded the H index threshold for reporting of potassium. In 75 intraoperative blood gas samples with H index and whole blood potassium and ionized calcium measured; we observed no relationship between H index and potassium or ionized calcium. During period 3 we switched to visual assessment of hemolysis with a greater tolerance for hemolysis; with only 3 of 5345 (0.06%) samples exceeding the new visual hemolysis threshold. CONCLUSION: For blood gas samples collected intraoperatively, there is no relationship between hemolysis and measured potassium or ionized calcium. The results suggest that only grossly hemolyzed intraoperative blood gas samples should be rejected for measurement of whole blood potassium and ionized calcium.

Comparing analytical outliers and the percent of emergency department patients with results above the 99th percentile upper reference limit for 2 conventional and one high sensitivity troponin assay.

OBJECTIVES: We compared rates of analytical outliers, and percent of emergency department (ED) patients with cardiac troponin (cTn) values above the 99th percentile upper reference limit (URL), for two conventional and one high sensitivity cTn assay. METHODS: We measured 3008 samples from 1931 ED patients by Roche e411 4th generation Troponin T (cTnT); and Abbott STAT Troponin I (cTnI) and high sensitivity troponin I (hscTnI) on an Architect i2000. Within 24h of initial measurement, samples were aliquoted, re-centrifuged, and repeated in duplicate by all methods. Outliers were defined as one or both replicates exceeding initial value by a critical difference (CD): where CD=z×2×SDanalytical (z=3.29 at a probability of 0.0005), and at least one replicate on a different side of 99th percentile URL compared to initial value. We also assessed percent of ED patients with values >99th percentile by all methods (excluding outliers), using both sex-neutral and sex-specific hscTnI URL. RESULTS: The outlier rate for cTnI (3.66%) was significantly higher than the outlier rate for either cTnT (0.33%) or hscTnI (0.47%) (p<0.0001). More ED patients (33%) had elevated cTnT values compared to either cTnI (25%) or hscTnI (29%). Application of sex-specific URL did not change the percent of ED patients with >99th percentile hscTnI values. CONCLUSION: Abbott STAT cTnI had more analytic outliers than Roche cTnT or Abbott hscTnI. Compared to cTnT, use of hscTnI will significantly decrease the percent of ED patients with elevated cTn values without increasing analytical outliers.