Abbott High Sensitivity Troponin I Assay
From 15 April 2019 Clinpath Pathology changed its Troponin assay from high-sensitivity troponin T (TnT) to high sensitivity troponin I (TnI).
This changeover was as a result of new state-of-the-art instrumentation deployed throughout all Clinpath laboratories.
The new TnI assay offers excellent sensitivity with reported values down to 2ng/L, well within the reference range for both male and female patients (<26ng/L and 16ng/L respectively).
Furthermore, TnI is more specific to cardiac muscle than TnT.
The increased sensitivity of the TnI assay enables its use in early ‘rule-out’ algorithms, to exclude acute coronary syndrome (ACS) in patients presenting to emergency centres with recent chest pain.
For instance, patients arriving at the emergency centre with suspected non-ST elevation myocardial infarction (NSTEM) can have this condition excluded at presentation if the TnI is 2ng/L or if the level at time 0 hours is <5ng/L with the change after 1 hour being less than 2ng/L
The negative predictive value in studies of acute coronary syndrome (ACS) assigned to the exclusion/’rule-out’ category exceeded 98% in several large studies. Used together with clinical and ECG findings, the 0h/1h algorithm can allow the identification of candidates for early discharge and outpatient management. Appropriate caution with ‘rule-out’ rules is still required for patients with suspected unstable angina pectoris.
The positive predictive value for myocardial infarction (MI) in those patients meeting the ‘rule-in’ criteria was 75-80%. Thus a patient on presentation with a TnI of 52ng/L or greater has a 75 to 80% chance of having ACS. If the TnI level increases by 6ng/L or more after one hour then the likelihood is even greater.
For patients with elevated TnI at presentation (ie > 26ng/L in men or > 16ng/L in women) a delta change of 30% after three or more hours is still required for confirmation of an NSTEMI.
As with all troponin assays there may be multiple causes for a troponin elevation other than ACS and results must be interpreted in the clinical context. Values of TnI however, tend to climb much higher following an MI, than those of TnT.
In general practice, if a patient presents with suspicion ACS or MI, a TnI or ECG should be requested. TnI values at this presentation, if greater than 50ng/L, should be regarded as clinically significant.
From 15 April 2019 requests for TnT will be processed as TnI. Further queries should be directed to myself.
Dr Devika Thomas
Director Chemical Pathology
Phone: 08 8366 2063