High-sensitivity troponin I (hsTnI) assays are now available from several vendors. There are now dozens, if not hundreds, of clinically-relevant studies published on these newer assays. These assays should not be confused with the standard troponin assays in routine use at all hospitals. These new assays can be over ten times more sensitive than the traditional troponin assays.
The term “high sensitivity” reflects these newer assay's lower limits of detection, it does not refer to a difference in the form of cardiac troponin being measured: these assay measure the same troponin molecule. The term "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 clinical specificity will decrease. If we can now detect troponin in seemingly healthy patients we will no longer be able to think of troponin as a qualitative 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. Clinicians will need to become familiar with using hsTnI on a much wider quantitative scale, across a larger spectrum of patients, from patients with frank AMI to those with subclinical, mild 'pre-ischemia' who are only at risk for AMI.
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 myocardial tissue. In 2007 the first high sensitivity troponin assay was FDA-approved in the US. Use of these new generation of tests is expected to spread in the coming years.
