Kaleta, Erin

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.

Abstract Background Cardiac troponin (cTn) assays are used for the diagnosis of acute myocardial infarction and frequently require serial measurements. Recollection of unacceptable specimens for hemolysis can delay results and disrupt timing of serial measurements. This study was designed to assess the influence of hemolysis on a high-sensitivity cTnT assay in granular detail at clinically important concentrations. These were used in consultation with the clinical practice to evaluate risk-based thresholds for acceptable amounts of hemolysis. Methods Plasma pools ranging from &lt;10 to &gt;100 ng/L cTnT were spiked with hemolysate to various degrees of hemolysis and measured using the Elecsys Troponin T Gen 5 STAT assay. The impact of accepting expanded hemolysis thresholds was completed using retrospective data of 12225 serial cTnT results and an additional 4651 baseline cTnT results. Results The mean percent change in cTnT was consistent for a given degree of hemolysis regardless of the initial nonhemolyzed cTnT concentration. Tiered hemolysis thresholds were evaluated for low-risk patients (apparent cTnT ≤8 ng/L), intermediate-risk patients (thresholds for 9–37 ng/L, 38–66 ng/L, and 67–99 ng/L cTnT), and high-risk patients (≥100 ng/L cTnT). The influence of tiered hemolysis thresholds was calculated for patients with serial (0 and 2 h) cTnT results, which demonstrated that the majority of 2-h delta interpretations were unchanged. Implementation of tiered thresholds dramatically decreased recollections for hemolyzed cTnT samples. Conclusion Tiered hemolysis cutoffs minimized disruption to patient care for low- and high-risk patients, while maintaining the integrity of serial measurements for those with intermediate cTnT concentrations.

SUMMARY Within the past decade, clinical microbiology laboratories experienced revolutionary changes in the way in which microorganisms are identified, moving away from slow, traditional microbial identification algorithms toward rapid molecular methods and mass spectrometry (MS). Historically, MS was clinically utilized as a high-complexity method adapted for protein-centered analysis of samples in chemistry and hematology laboratories. Today, matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) MS is adapted for use in microbiology laboratories, where it serves as a paradigm-shifting, rapid, and robust method for accurate microbial identification. Multiple instrument platforms, marketed by well-established manufacturers, are beginning to displace automated phenotypic identification instruments and in some cases genetic sequence-based identification practices. This review summarizes the current position of MALDI-TOF MS in clinical research and in diagnostic clinical microbiology laboratories and serves as a primer to examine the “nuts and bolts” of MALDI-TOF MS, highlighting research associated with sample preparation, spectral analysis, and accuracy. Currently available MALDI-TOF MS hardware and software platforms that support the use of MALDI-TOF with direct and precultured specimens and integration of the technology into the laboratory workflow are also discussed. Finally, this review closes with a prospective view of the future of MALDI-TOF MS in the clinical microbiology laboratory to accelerate diagnosis and microbial identification to improve patient care.