Dr Graham Jones
Department of Chemical Pathology

Troponin

Cardiac-Specific troponins

Troponin I can be detected in the blood stream in elevated amounts following any cause of damage to myocardial cells. The test is commonly used in the setting of chest pain to confirm a clinical suspicion of acute myocardial infarction.

The troponin assay at  SydPath :
·       At SydPath we use the Siemens Centaur analyser which provides accurate troponin I measurements down to very low concentrations.
·       The lowest result that can be measured is 0.03 ug/L and values below this are reproted as less than 0.03 ug/L (<0.03).
·       The reference interval is < 0.06 ug/L which is set as the 99th centile of a healthy population.

The clinical effects of this highly sensitive assay are as follows:
·       A negative troponin has a good ability to exclude heart damage.
·       The assay will detect cardiac damage earlier than less sensitive assays. Troponin elevations may be seen as soon as 2 – 3 hours after onset of chest pain in some patients.
·       After cardiac damage troponins can be detected for longer than in less sensitive assays.
·       More cases of low-level troponin elevations will be detected compared less sensitive assays.

Interpretation

The sensitive troponin assay identifys more cases of acute coronary syndrome (ACS), where the troponin rise indicates an increased risk of subsequent events. There are also more cases of small troponin elevations due to other causes. A patient should only be diagnosed with ACS if the clinical setting and patient history supports the diagnosis. A rise and fall pattern in serum troponin also supports a diagnosis of ACS while many other causes, particularly non-ischaemic causes, commonly show a stable low-level elevation. Other causes of elevated troponins are shown below. A positive troponin in the absence of a clinical condition likely to cause the rise should be discussed with the laboratory.

Causes of elevated serum troponins

1.    Acute coronary syndrome – ischaemic myocardial damage due to coronary artery disease. Includes ST elevation myocardial infarction (STEMI) and Non-ST elevation myocardial infarction (non-STEMI).

2.    Other ischaemic causes of cardiac damage. Examples include: cardiac arrest, angioplasty and stenting, cardiac surgery, shock from any cause, severe heart failure, cocaine abuse, pulmonary embolism, tachy-arrythmias.

3.    Non-ischaemic causes. Examples include: myocarditis, pericarditis, end-stage kidney disease (eg dialysis dependent), direct cardiac trauma, drug toxicity (eg doxorubicin).

Reference Interval

The reference interval for the new assay of < 0.06 ug/L is the 99^th centile of a healthy population. This decision point has been recommended for the definition of myocardial infarction (see references). Any troponin elevation above this level in the setting of acute coronary syndrome carries adverse prognostic significance.

References

• Guideline for the management of acute coronary syndromes 2006. Med J Aust 2006;184 supplement.
• A consensus document of the joint European Society of Cardiology / American College of Cardiology committee for the re-definition of myocardial infarction. J Am Coll Cardiol 2000;36:959-969.

Tube Type:
A lime-top (heparin) tube is the preferred tube for troponin measurements on hospital inpatients (and is required for samples from ED, CCU or patients receiving heparin), although a gold-top (serum) tube is acceptable for samples collected off-campus.