What is Troponin?
Troponin is a muscle protein that is released into the circulation following Acute Myocardial Injury (AMI). Troponin assays are now available for Trop I and T levels at varying degrees of sensitivity with very high sensitivity tests now available and in regular use. Both laboratory and point of care (POC) tests are available. POC tests at the time of writing are generally "standard" sensitivity but this is a rapidly evolving area and very high sensitivity tests are currently being tested.
Who should have a Troponin test?
Those patients with suspected acute coronary syndrome (ACS) should have a troponin test. The troponin test should be used as part of a clinical management pathway.
Management should not be delayed whilst waiting results. The troponin assay should be used in conjunction with your clinicial assessment of ACS patients.
When to measure Troponin?
When patients present with chest pain or symptoms suspicious of Acute Coronary Syndrome patients should be put on a Pathway and a troponin measured at zero hours. This should be followed by a repeat troponin at a designated time depending on the assay being used. Current advice is at 2 hours for high sensitivity troponins and 6-8 hrs for standard sensitivity and POC tests such as iSTAT.
What to do with the result?
Troponin results should always be interpreted within the context of the entire clinical presentation and combined with at least 2 correctly interpreted ECGs.
Troponin levels are usually presented as:
- Below lower limit of detection
- Detected and within the 99th centile (normal range)
- Above the 99th centile (elevated)
The delta troponin is the change from the first to the second (or third) troponin. The size of the change which represents a significant change and therefore indicating AMI varies with assays and from place to place. Some places for example, will use absolute values and some percentage values. The risk in using percentage values is when the troponin is initially raised for reasons other than ACS an otherwise significant rise might be misinterpreted. Note that chronically elevated levels of troponin are a representation of “steady state” and any acute changes reflect acute release and therefore ACS.
When there is suspicion of ACS a single troponin is never done.
What are the non-ACS causes of Troponin elevation?
Many conditions other than MI can cause an increase in Troponin concentration. These include;
- Acute sepsis – reduced coronary perfusion
- Pulmonary embolism – Muscle stretch
- Stable coronary artery disease - with relative reduced perfusion
- Congestive CCF - reduced perfusion, stretch
- Inflammatory diseases e.g. pericarditis, myocarditis-muscle injury
- Aortic dissection- +/- coronary perfusion affected.
- Renal failure- decreased excretion
- Chronic heart disease.
Further References and Resourcess
Chew, D, et al. (2011) 2011 Addendum to the National Health Foundation of Australia / Cardiac Society of Australia and New Zealand Guidelines for the Management of Acute Coronary Syndromes (ACS) 2006, Heart, Lung and Circulation, vol. 20, pp. 487-502.
National Heart Foundation (NHF) of Australia / Cardiac Society of Australia and New Zealand Guidelines for the Management of Acute Coronary Syndromes - Updated September 2016.
- Troponins - John Mackenzie, ECI Medical Officer at the ECI ED Leadership Forum 9 June 2017
- Point of Care Troponins - Brian Heffernan, Point-of-Care Program Coordinator, NSW Pathology at the ECI ED Leadership Forum 9 June 2017