Evaluating Tiered Hemolysis Thresholds to Facilitate Rapid Reporting of High-Sensitivity Cardiac Troponin

Rapid serum tubes reduce transport hemolysis and false positive rates for high-sensitivity troponin T

INTRODUCTION

Hemolysis in the emergency department (ED) can significantly delay results and appropriate action. We evaluated the main sources of hemolysis during sample collection, and to evaluate the use of rapid serum tubes (RST) as a transport hemolysis-mitigating measure for high-sensitivity troponin T (hs-cTnT) testing.

METHODS

We examined the effect of tube type, tube fill, types of sample draw and collection methods on hemolysis and hs-cTnT in samples (n = 158) from ED patients. We also compared hs-cTnT values in paired RST and plasma separate tube (PST) samples that were hemolysis-free.

RESULTS

The primary source of hemolysis in samples collected in the ED was underfilling tubes. In both tube types, PST and RST, filled tubes showed a median reduction in hemolysis of 69.1 % (p < 0.0001). Blood collected in RST also experienced less hemolysis compared to PST. In hemolysis-free samples, false positive results in PST were noted in patients with hs-cTnT values < 50 ng/l.

CONCLUSION

We suggest that proper tube filling during sample collection and use of RST tubes can significantly reduce the effects of hemolysis. In addition, laboratories should be aware that PST tubes have a non-trivial rate of false positives when hs-cTnT < 50 ng/l.

Flexible-Interval High-Sensitivity Troponin Velocity for the Detection of Acute Coronary Syndromes

Many algorithms for emergency department (ED) evaluation of acute coronary syndrome (ACS) using high-sensitivity troponin assays rely on the detection of a "delta," the difference in concentration over a predetermined interval, but collecting specimens at specific times can be difficult in the ED. We evaluate the use of troponin "velocity," the rate of change of troponin concentration over a flexible short interval for the prediction of major adverse cardiac events (MACEs) at 30 days. We conducted a prospective, observational study on a convenience sample of 821 patients who underwent ACS evaluation at a high-volume, urban ED. We determined the diagnostic performance of a novel velocity-based algorithm and compared the performance of 1- and 2-hour algorithms adapted from the European Society of Cardiology (ESC) using delta versus velocity. A total of 7 of 332 patients (2.1%) classified as low risk by the velocity-based algorithm experienced a MACE by 30 days compared with 35 of 221 (13.8%) of patients classified as greater than low risk, yielding a sensitivity of 83.3% (95% confidence interval [CI] 68.6% to 93.0%) and negative predictive value (NPV) of 97.9% (95% CI 95.9% to 98.9%). The ESC-derived algorithms using delta or velocity had NPVs ranging from 98.4% (95% CI 96.4% to 99.3%) to 99.6% (95% CI 97.0% to 99.9%) for 30-day MACEs. The NPV of the novel velocity-based algorithm for MACE at 30 days was borderline, but the substitution of troponin velocity for delta in the framework of the ESC algorithms performed well. In conclusion, specimen collection within strict time intervals may not be necessary for rapid evaluation of ACS with high-sensitivity troponin.

Reducing Specimen Rejection Rates Using Concentration-Dependent Hemolysis Rejection Thresholds

BACKGROUND

Using middleware solutions, it is possible to implement concentration-dependent analyte-specific hemolysis rejection limits. This makes day-to-day reporting of clinical specimens more efficient and potentially lowers sample rejection rates compared to a "one-size-fits-all" approach (i.e., solely based on a single cutoff provided in the package insert).

METHODS

Hemolysis interference studies were performed at multiple analyte concentrations for three frequently ordered tests. For each assay, concentration-dependent hemolysis rejection limits were designed based on the total allowable error (TAE) for the analyte as well as the clinical significance of such incurred inaccuracy at the respective concentrations. In general, the following rationale was used: if the interference exceeds 10% (or package insert cutoffs), a comment is placed on the result. If the interference exceeds the TAE, the result will not be reported. Reduction in specimen rejection rates were estimated by comparing the incurred specimen rejection rates when package inserts' vs concentration-dependent hemolysis interference limits were applied to a data set in our institute during a three-month period.

RESULTS

Concentration-dependent analyte-specific hemolysis rejection thresholds were designed for three commonly ordered assays that are especially susceptible to hemolysis interference. It is estimated that these novel thresholds for aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and direct bilirubin (DBIL) reduced specimen rejection rates from 9.3% to 1.3%, 31.4% to 4.8%, and 19.9% to 7.1%, respectively.

CONCLUSIONS

Concentration-dependent analyte-specific hemolysis rejection thresholds for three commonly ordered assays can reduce rejection rates without significantly compromising the quality of test results.

Analytical and Clinical Considerations in Implementing the Roche Elecsys Troponin T Gen 5 STAT Assay

OBJECTIVES

To evaluate the analytical and clinical performance characteristics of the fifth-generation troponin T reagent.

METHODS

Troponin T was measured in 2,332 paired serum and plasma samples from emergency department and hospital patients using the fourth- and fifth-generation reagents. Testing was repeated after recentrifugation to determine the frequency of analytical outliers and percentage of patients with elevated values for each assay. We conducted separate experiments to determine the effects of biotin and hemolysis interference, as well as measure interinstrument variability, for fifth-generation troponin T.

RESULTS

Analytic outliers occurred more frequently using the fifth-generation reagent (3.4%) compared with the fourth-generation reagent (1.0%). The frequency of elevated troponin T above the 99th percentile upper reference limit was 26% for the fourth-generation reagent and 52% for the fifth-generation reagent. Clinically significant assay interference by biotin was observed at 20 ng/mL, but hemolysis interference was not observed until an H index of 150. Instrument-to-instrument variability between e411 and e601/602 instrument platforms is predicted to confound clinical interpretation of troponin changes.

CONCLUSIONS

Analytical outliers and instrument-to-instrument variability are the two analytical variables most likely to confound interpretation of changes in fifth-generation troponin T results over time.

Laboratory-related issues in the measurement of cardiac troponins with highly sensitive assays

A number of assay-related issues can affect the performance of cardiac troponin (cTn) measurement in everyday practice. In this respect, it is vital that all information on cTn assays is known and that the performance characteristics of assays are objectively assessed and adequately described. The advent of the latest generation of more sensitive cTn assays has heralded a new wave of information about low concentrations of cTn in blood. These recent generation assays have improved analytical sensitivity and corresponding performance at low cTn concentrations when compared to their predecessors, providing a convincing goal for laboratory medicine in helping clinicians in the diagnosis of acute myocardial infarction. Crucial to the clinical utility of highly sensitive cTn assays is the laboratorians' role in closely scrutinizing proposed assays and defining their value in relation to available evidence. Analytical, as well as pre-analytical and post-analytical, aspects must be documented. In this review, we describe what laboratory professionals should know about their cTn assay performance characteristics and the pre-analytical prerequisites for robustness to ensure optimal post-analytical reporting.

Establishing hemolysis and lipemia acceptance thresholds for clinical chemistry tests

BACKGROUND

A key component of laboratory medicine is the evaluation of specimen suitability for downstream analytical testing. Accurate identification and characterization of the impact of interferents on clinical chemistry analytes is important for patient care. To empirically assess the influence of hemolysis and lipemia on clinical chemistry tests analyzed on a Roche cobas® c701 system, we evaluated serum pools spiked with increasing concentrations of hemolysate and Intralipid®.

METHODS

Using an interferent acceptance threshold of within ± 10% of the non-hemolyzed or non-lipemic results, 31 routine chemistry analytes were evaluated.

RESULTS

The majority of analytes were determined to have the same or very similar acceptability thresholds as those listed in the vendor package insert. However, several analytes resulted in new thresholds that deviated from manufacturer recommendations (9 higher and 2 lower for lipemia, 7 higher and 6 lower for hemolysis). Samples with high enzyme activities (LDH, ALT, AST, ALP, and CK) were observed to tolerate higher levels of hemolysis, and tiered hemolysis thresholds were established for these enzymes. Independent evaluation of indices is recommended to enable thoughtful implementation of specimen quality criteria and to provide guidance to laboratorians and providers on the nature of these interferences.