Troponin 1 Testing
(December 2003)
(Download 
Troponin 1 Testing.pdf)
Changeover Date to New Range and Methodology: 11am Wed 30th January, 2003
Cardiac Troponins I and T have been introduced over the last few years as specific markers for myocardial cell necrosis. All HAPS laboratories in the Hunter Valley have been measuring Troponin I by a particular methodology (DPC Immulite) that:
- Gives values of <0.2 ng/mL for the vast majority of normal samples, but
- Values between 0.2 and 1.0 ng/mL are in a grey area without clear interpretation.
- Values over 1.0 ng/mL are interpreted as showing some myocyte necrosis, and most ECG positive myocardial infarcts ultimately show values in excess of 20 ng/mL, with the highest we have recorded at >1000 ng/mL.
We have recently tested a different analyser (Beckman-Coulter Access II) with a different reagent formulation for the measurement of Troponin 1 that has also been extensively trialed in other pathology laboratories. The method has been reported to have superior performance.
- With this method the upper range of normal samples is 0.04ng/mL.
- There is a very small grey area so that results in excess of about 0.05ng/mL suggest traces of myocyte necrosis.
Our own comparison with the older method leads us to suggest at this state that:
- Values between 0.04 and 0.1ng/mL should be interpreted as "uncertain".
- Values > 0.1ng/mL should be interpreted as showing some myocyte necrosis.
In cases of clear myocardial infarction, the levels with this new method are found to be approximately one half to two thirds as high as with our older method. We will continue to monitor results in an attempt to narrow the "uncertain" zone.
This superior performance of the new test is due to the development of superior combinations of monoclonal antibodies, which react to different extents with the intact and the several partially degraded forms of Troponin I that are found in circulating blood, and non-specifically with other blood components. The performance of this new assay is as good as that reported in the literature for Troponin T quantitative assays.
The new methodology does not alter in any way the rules agreed for performance of Troponin I measurements, namely
- Not less than 8-hours post onset of episode to exclude necrosis.
- The refusal of repeat levels once one is positive, unless agreed by the duty biochemist.
- The recommendation NOT to measure Troponin if there is certainty that there has been an infarct, especially after thrombolysis.
All HAPS laboratories propose to change to the new analyser and reagent at 11am on Wednesday 29th January, when the new analysers in JHH and Maitland laboratories have been installed and staff trained. Until then we will continue with the current method. We will alert users of our service by a note on the bottom of all reports with troponin results when the new method is commenced.
It is emphasised that no test - troponin or otherwise - gives a diagnosis of myocardial infarction. The test indicated myocardial cell necrosis, and while this is overwhelmingly due to ischaemia and subsequent infarction, there are other causes especially of small rises in troponin. These include various toxic effects such as sepsis, snake bite, severe hypoxia, possibly some drugs, other forms of myositis etc.
About the Author
This HAPS Communique was written by Dr Phil Tynan , Former Clinical Chemistry Staff Specialist
If you have any questions regarding this topic Clinical Chemistry can be contacted on Telephone: (02) 49214000, Facsimile: (02) 49214400.