Abstract
Cardiac troponin T (cTnT) assays are used for the diagnosis of acute myocardial infarctions and require serial measurements. Hemolysis is a common analytical interference for cTnT immunoassays, causing a false decrease in analyte concentration. Recollection of specimens that do not meet the recommended hemolysis threshold (H-index = 100) causes reporting delays and mistiming of serial measurements. This has been particularly disruptive to our emergency department and creates significant risk for patients whose diagnosis could be delayed by recollection due to hemolysis. Here we aimed to reevaluate the limits for acceptable hemolysis by determining the magnitude of cTnT concentration depression from hemolysis to evaluate whether more detailed thresholds could be established. To quantify the effects of hemolysis on cTnT, patient pools were prepared from residual serum with cTnT concentrations ranging from 10 to 100 ng/L and spiked with hemolysate prepared from lysed red blood cells to create H-indices ranging from 120 to 200. Samples were run in triplicate by the Elecsys Troponin T Gen. 5 STAT assay. Results demonstrated consistent percent decreases in cTnT across all concentrations tested for each level of hemolysis. The mean percent changes in cTnT concentrations in the presence of hemolysis for H-indices of 120, 140, 160, 180, and 200 were –3.4 ± 1.3%, –4.1 ± 1.2%, –6.3 ± 1.2%, –8.0 ± 1.7%, and –10.7 ± 1.22%, respectively. The observed decrease in cTnT was linearly related to the H index; predicted differences at higher H-indices (>200) agreed well with prior publications evaluating greater degrees of hemolysis. In our practice, a 2-hour delta ≥10 ng/L is considered significant for acute cardiac injury, <4 ng/L is a nonsignificant delta, and a delta of 4 to 9 ng/L is considered indeterminate. Baseline cTnT results of ≥100 ng/L result in immediate triage to cardiology. Approximately one-third of our patients with cTnT testing have baseline results within the reference range (≤15 ng/L males, ≤10 ng/L females). Based on the spiking data, H-index cutoffs were chosen to minimize recollections for low-risk and high-risk patients. Cutoffs for intermediate cTnT results were more restrictive to ensure delta interpretation would not change significantly. This resulted in a H-index of 300 for samples ≤8 ng/L, 200 for 9 to 40 ng/L, 160 for 41 to 70 ng/L, 140 for 71 to 99 ng/L, and 300 for ≥100 ng/L. These data quantify the percent change for cTnT in the presence of varying levels of hemolysis. At lower cTnT values, a larger degree of hemolysis can be tolerated because the percentage of depression results in a small absolute change, thus leading to less impact on the delta. The tiered H-index cutoffs allow minimal disruption to patient care for low- and high-risk patients, while maintaining the integrity of serial measurements for those with intermediate cTnT concentrations. Therefore, laboratories may consider releasing some hemolyzed cTnT specimens with a comment to decrease redraws and mistiming of serial measurements.
A Novel Index for Prompt Prediction of Severity in Patients with Unstable Angina Pectoris
