A-325 Overcoming hemolysis photometric interference on glucose results

Abstract Background Capillary blood samples that have been self- collected can potentially increase accessibility in regards to testing, however these samples are prone to increased hemolysis when exposed to various environmental conditions when shipped through the mail. Hemolysis drastically affects glucose measurements; therefore, we aimed to resolve this hemolysis interference, reducing the frequency of sample rejection due to inaccurate measurements. Methods All samples were run on the Roche cobas enzymatic glucose assay with hexokinase (GLUC3) on the c502, which automatically performs a hemolysis index. Initially, two tube types were compared. Five samples were tested for glucose and hemolysis levels before and after next-day shipping in sodium fluoride/potassium oxalate(NaF/K-Oxalate) and sodium fluoride/Na2EDTA(NaF/Na2EDTA) collection tubes. Secondly, a dose response interference study was performed according to CLSI document EP7-A to determine the impact of hemolysis levels on the glucose measurement. A known sample measuring 106.4mg/dL glucose was spiked with different amounts of hemolysis (0, 1976, 3140. 6280, 9420, 12561mg/dL) and run in replicates of 3 for each level. Finally, a dilution integrity study was performed to see if the interferant (hemolysis) could be overcome by diluting it out. One sample underwent dilution at 1:5 at varying levels of hemolysis (0, 1250, 2500, 3750, 5000mg/dL) both manually and on-board. Results Comparing before-shipping and after-shipping results, there was an overall bias of -0.12% or ± 3.88 mg/dL in NaF/K-Oxalate and 3.53% or ± 5.44mg/dL in NaF/Na2EDTA. Average hemolysis levels were 4201 mg/dL after shipping in NaF/K-Oxalate and 1168 mg/dL in NaF/Na2EDTA. The biases determined at hemolysis concentrations of 0, 1976, 3140, 6280, 9420, 12561mg/dL for the sample measuring 106.4 mg/dL for glucose were 0, 6.58, 12.28, 20.37, and 27.89%. By establishing a regression line, this data shows that the bias remains clinically non-significant at hemolysis concentrations less than 1667.4mg/dL when using 50 percent of the known allowable error budget of or 6mg/dL or ± 10%. The biases of a patient tube with glucose 99.38 mg/dL with hemolysis levels 0, 1250, 3750, and 5000mg/dL without a dilution are 0.00, 2.54, 6.40, 10.77, and 13.89%. The bias after applying the 1:5 dilution became 0.00, 0.10, 0.37, 0.24, and 2.21%. Overall, the accuracy and precision(CV%) of the 1:5 on-board dilution (n=25) and the manual dilution (n=25) was 102.57%(1.00%) and 103.24% (2.21%) respectively. Conclusions Lower hemolysis levels were seen in NaF/Na2EDTA. Glucose measurements remain accurate when hemolysis levels are below 1667.4 mg/dL, which extends the range of samples that would normally be accepted according to the manufacturer’s instructions (up to 1000 mg/dL). In addition, samples with hemolysis between (1667.4 -7476.75mg/dL) can be diluted (1:5) to overcome the interference caused by hemolysis. In summary, these data show that rejection rates of mailed samples due to hemolysis can be reduced.