Abstract
Background
High sensitivity troponin assays were developed to improve analytical sensitivity and precision at the decision cut-points for the diagnosis and rule out of acute myocardial infarction (AMI). Central laboratory assays have achieved this but point of care assays, which have the ability to accelerate decision making due to much shorter turnaround times, have remained lacking.
Purpose
To ascertain the threshold for decision making and subsequent clinical utility for ruling out AMI on presentation in patients attending the emergency department acutely with chest pain, using a high precision point of care troponin assay (TnI Nx), (i-STAT, Abbott).
Methods
We measured arrival TnI-Nx concentrations in stored plasma samples in adults presenting acutely to the emergency department with chest pain. The primary outcome was an AMI or cardiac death on index admission or within 30 days. We used 2000 bootstrapped data sets to derive and validate a suitable threshold for TnI-Nx before calculating diagnostic test performance. We pre-specified this threshold must have a <1% false negative rate for the primary outcome. We compared this with a core laboratory high sensitivity troponin I (hs-TnI) (Abbott Architect) using the early rule-out cut-point (European Society of Cardiology) at the limit of detection (2 ng/L).
Results
We recruited 1320 patients of whom 192 (14.1%) had the primary outcome. The TnI-Nx threshold was determined to be 8 ng/L with subsequent sensitivity of 99.0% (95% confidence interval: 97.3% to 100%), negative predictive value of 99.7% (99.2% to 100%) and specificity of 59.0% (56.0% to 62.0%). The hs-TnI had a sensitivity of 99.5% (98.2% to 100%), negative predictive value of 99.7% (99.0% to 100%), and specificity of 28.4% (25.8% to 31.2%) at 2ng/L.
Conclusion
A high precision point of care assay, TnI-Nx, with a decision threshold of 8ng/L, has comparable rule out performance compared with a core laboratory high sensitivity assay and therefore could potentially be used for early decision making in the assessment of acute chest pain.
Acknowledgement/Funding
Research grant from Abbott Point of Care. Senior Research Fellowship from ECF, CMRF and CDHB. Clinical Research Fellowship from NZ HRC
Fitting a Square Peg in a Round Hole: A Simple Case of Chest Pain
