Troponin I: guide for primary care

Procedure for requesting Troponin I

Take sample in Red EDTA tube and note time taken and time of onset of symptoms.

The sample must be processed within 4 hours of being taken.
Contact the Lab (9-5 Mon-Fri, 9-12 Sat-Sun). Out with these hours contact A+E to run the sample (OUAB and St Brendan’s also have access to POC testing on site)
Ensure that you leave clear instruction of where the result should be telephoned to.
For Interpretation see
- Intranet> Shared Clinical Guidelines Homepage> Top Left Red Box ‘Trop I Algorithm’.

What is it?

Troponin I is a cardiac specific protein. Any cause of myocyte damage will release troponin I. It does not indicate the mechanism of myocyte damage.
Troponin I using the current lab High Sensitivity method will be detectable in the blood in 1 hour after injury.

Reasons for a raised level

Troponin I will be raised by any condition that causes myocyte damage. It is therefore a very NON-SPECIFIC test for Myocardial Infarction but is also very sensitive. Examples of conditions that can raise Troponin I include:

Heart Failure (Acute or Chronic)
Tachy/Brady arrhythmias (e.g. Fast AF, SVT)
Hypertrophic Cardiomyopathy
Hypertension
PE
COPD
Renal Impairment

Troponin I in Myocardial Infarction (MI)

Troponin I can aid a diagnosis of MI but must never be used in isolation to do so
MI evaluation and diagnosis requires careful clinical evaluation and ECG analysis as well as assessment of cardiac biomarkers such as Troponin I
As Troponin I can be persistently raised in many individuals (e.g. with renal impairment or heart failure), the diagnosis of myocardial damage requires a dynamic change in Troponin I in the blood. Therefore, myocardial damage can only be reliably diagnosed by taking TWO readings separated by a time interval. A single raised reading is insufficient to exclude myocardial damage in most cases.
A single reading taken more than 3 hours after an episode of chest pain however can reliably rule out Myocardial Infarction if it is not raised as Troponin I becomes detectable by about 1 hour following Myocardial Damage.

Requesting Troponin I in the community

With very few exceptions (examples below), Troponin I should only be requested in a secondary care
Examples of when it may be appropriate to request a Troponin I in primary care would include:
- A patient with an equivocal history who is deemed unsuitable for transfer for PCI or ‘Intensive’ treatment but in whom knowledge of a recent MI would allow appropriate treatment to be commenced
- A stable patient who presents ‘late’ after an episode of chest pain who declines admission but in whom a Troponin I result confirming MI would affect treatment/refer