The newer, highly-sensitive troponin assays have their pitfalls. Specifically, specificity. However, most of the issues associated with diminished specificity are iatrogenic – transitioning from use of troponin as a dichotomous test that used to tell us “yes” to one that does a better job of telling us “no”.
This is a pre-planned substudy as part of a prospective evaluation of patients with chest pain and non-diagnostic ECG, prospectively evaluated for acute coronary syndrome. These authors looked at hsTnI, but, rather than using the 99th percentile as their cut-off for “negative”, they evaluate the utility of an undetectable hsTnI – which, for this Siemens assay, was <0.006 µg/L. Based on 1,076 patients evaluated, 647 had an undetectable troponin at initial presentation. Of these, 4 patients had a subsequently detectable troponin and were adjudicated as acute MI, 3 of which had coronary artery disease and received revascularization.
What was special about those four patients? Each of them presented within 2 hours of symptom onset. All told, 399 patients presented more than 2 hours after the onset of symptoms, had an undetectable troponin, and were free of MACE at 7 and 30 days. These results are generally consistent with other work looking at the sensitivity of the (duh) highly-sensitive troponin assays – capable of conferring an excellent instant rule-out.
So, if you’re asking the question – does this patient have an acute MI? – you’re in good shape. However, if you’re using highly-sensitive troponin assays, you’ll also need to be smart about appropriately interpreting the indeterminate range – or your patients will ultimately suffer as a result of decreased specificity and downstream over-testing. Lastly, this is only valid as a diagnostic tool for acute MI – the extent to which it provides prognostic or diagnostic information regarding acute coronary syndromes, coronary artery disease, or ischemic heart disease is still being refined.
“Does undetectable troponin I at presentation using a contemporary sensitive assay rule out myocardial infarction? A cohort study”
http://www.ncbi.nlm.nih.gov/pubmed/25552547
Are all troponin I assays today considered highly sensitive or it needs to be checked with the individual lab?
Check with your lab. The majority of assays are "conventional" troponin, still. Each has their own specific limit of detection and measure of precision at the limit.