High-sensitivity troponin I (hsTnI) assays are currently available from several vendors. There is also a high sensitivity TnT assay available. The term “high sensitivity” reflects the assay's characteristics and does not refer to a difference in the form of cardiac troponin being measured (we are measuring the same troponin molecule). Several names have been used in the literature for these new assays, including “high-performance,” “highly sensitive,” “high-sensitive,” “ultrasensitive,” and “high sensitivity" -it can be confusing. Although there is not consensus on the name, it has been proposed that high-sensitivity can be used to describe a troponin assay that has:
- Total imprecision (CV) at the 99th percentile that is ≤10%
- Measurable concentrations should be detectable below the 99th percentile in 50% of the population (that is, we should be able to measure troponin in half of otherwise 'normal patients').
Advantage of hsTn assays
These new high-sensitivity troponin assays have ten times the sensitivity of other cTnI and cTnT assays. Instead of having lower limits of detection around 0.01 ng/L, the new assays can detect down to 0.001 ng/L. Having this increased sensitivity means we will be able to detect smaller changes sooner. This will increase our sensitivity for cardiac damage. Indeed, studies are showing that we can detect cardiac issues before frank ischemia and necrosis even occur. Studies are showing that the hsTnI assays can be used to assess cardiac prognosis and even pre-cardiac event risk.
Disadvantage of hsTn assays
However this increased sensitivity comes at a price: the specificity will decrease. If we can now detect troponin in seemingly healthy patients we will no longer be able to think of troponin as an ACS/AMI cut-off marker. The paradigm of thinking that 'troponin is present when a person has dying heart tissue' needs to be revamped. These new assays are revealing that troponin is detectable in many patients, some of whom seem healthy. Thus, we will need new criteria and stricter reference ranges that help us hone in on true ischemia and infarcts.
Studies are being published frequently in this area. One thing is certain; high-sensitivity troponin assays will revolutionize the way we use cardiac biomarkers and how we assess the myocardium. But more work has to be done before these new assays can be incorporated into the well-established clinical algorithms and operations that emergency room physicians and cardiologists are used to.