Diagnostic Use
The troponin assay is specific for a cardiac isoform that occurs only in myocardium. The test is very specific and sensitive for myocardial damage, but there are many causes of such damage.
In myocardial infarction, elevated levels are detectable in blood within 4-6 hours after the onset of chest pain, reach peak concentrations in approximately 12 hours, and remain elevated for 3-10 days. The diagnosis of myocardial infarction cannot be made solely on the basis of an elevated troponin level; it requires a typical rise (or fall, if presentation is late) of troponin occurring in combination with typical symptoms of myocardial ischaemia and/or typical ischaemic changes on the 12 lead ECG.
In the acute coronary syndrome, a rise (or fall) of troponin by 50% or more during the course of the event is taken as significant, and should usually lead to further investigation of coronary circulation seeking a remediable stenosis.
Other causes of modest elevation of cTnI include:
Pulmonary embolism
Myocarditis and pericarditis
Chronic heart failure
Acute rhythm disturbance such as paroxysmal atrial fibrillation
Severe sepsis
Myocardial contusion
Extreme exercise (triathlon, marathon)
Some patients show elevation of troponin by a given assay whenever it is measured. The cause is believed to be interference in the assay by macrotroponin or by heterophilic (anti-mouse immunoglobulin) antibodies. The result usually varies by less than about 30% between measurements. If such interference is suspected, it can be confirmed by arrangement with the chemical pathologist or registrar who can arrange troponin measurement using a different assay.
Test Method
Principle: 3-site Sandwich Immunoassay
Reagents: Siemens Atellica IM High-Sensitivity Troponin I
Analyser: Siemens Atellica Solution (NSH) and Atellica CI (WTH)
Limitations / Interference
Patient samples may contain heterophilic antibodies that could react in immunoassays to give falsely elevated or depressed results.
Samples from patients receiving preparations of mouse monoclonal antibodies for therapy or diagnosis may contain human anti-mouse antibodies (HAMA). Such samples may show either falsely elevated or falsely depressed values when tested with this method.
Specimens from some individuals with pathologically high gamma globulin levels may demonstrate depressed cTnI values. This may be due to the presence of cTnI-specific autoantibodies.