The “highly sensitive” troponin has received a great deal of publicity, hyped ad nauseum, see: “Simple test could help rule out heart attacks in the ER.”
But, as sensitivity increases – invariably, specificity decreases. However, that is not the fault of the test – it is a failure of clinicians to ask the correct question of the test. When asking “does this patient have an acute myocardial infarction?”(most commonly Type 1 MI in the ED), our training and education has been outpaced by assay technology – the test no longer provides a dichotomous “yes” or “no”.
This publication provides a lovely window into precisely the added value of the hsTnI compared with conventional TnI, both assays by Abbott Laboratories. In this study, the authors simultaneously drew research samples of blood any time a cTnI was ordered. The sample was frozen, and then analyzed at least 1 month following presentation. Authors performed hospital records review, telephone follow-up, and vital records search to evaluate adverse events in patients with hsTnI or cTnI elevation.
Overall, they enrolled 808 patients, 40 of which received an adjucated diagnosis of “acute coronary syndrome” – 26 with AMI and 14 with unstable angina. 61 patients had acute heart failure, 7 had volume overload, 7 had pulmonary emboli, and 41 had other non-ACS cardiac diagnoses.
All told, there were 105 elevated cTnI samples – and 164 elevated hsTnI samples. This means, essentially – in the acute setting, asking our question of interest – there were 50% greater false positives associated with hsTnI. No patients would have been reclassified as nSTEMI based on the hsTnI result. The authors sum this up nicely in their discussion:
“The preponderance of novel elevations (roughly 10% in this study) will be observed mainly in subjects with non-ACS conditions.”
The authors go on to note the value in detecting these novel or detectable troponin levels – essentially, non-ACS, subclinical disease – with a much poorer long-term prognosis. This is almost certainly the case, although it will require further investigation to reliably demonstrate cost-effective management strategies based on these results.
“Troponin Elevations Only Detected With a High-sensitivity Assay: Clinical Correlations and Prognostic Significance”
http://www.ncbi.nlm.nih.gov/pubmed/25112512
Addendum: As Stephen Smith points out, it may be possible to use the greater precision of hsTnI at the low end of the assay to more accurately adjudicate some MI. Great insight!