Laboratory medicine switched from the Troponin I assay to
a highly sensitive Troponin T assay. This change coincided
with the introduction of the new ACS pathway, and all information
on that pathway refers to the new assay. The major changes were as
follows:
- The assay measures Troponin T rather
than Troponin I
- Reporting Units changed from micrograms
per litre (ug/L) to nanograms per litre (ng/L)
- The cut-off for ACS which was 0.05 ug/L with
the Troponin I assay has become 30 ng/L with the Troponin T
assay
- Troponin T is the first routine Troponin
assay to be able to detect Troponin in normal individuals, and so a
lower cut-off will also be reported which is the 99th centile of
the normal distribution and is 14 ng/L. Results between 14 and 30
ng/L are abnormal, but the clinical implications are less well
established than for results > 30 ng/L. There are other causes
of an elevated Troponin which should also be considered. See
below.
- Because of the improved assay sensitivity,
the timing of samples has changed. Samples should be taken on
admission (or at the time of an event) and then repeated (if
necessary " see ACS protocol) at 6 hours after the event or
symptom onset. This is instead of the previous recomendation of 12
hours.
Causes of elevated Troponin in the
absence of overt ischaemic heart disease:
- Congestive heart failure"acute and chronic
- Pulmonary embolism, severe pulmonary hypertension
- Rhabdomyolysis with cardiac injury
- Inflammatory diseases, e.g. myocarditis or myocardial extension
of endo-/ pericarditis
- Infiltrative diseases, e.g. amyloidosis, haemochromatosis,
sarcoidosis, and scleroderma
- Critically ill patients, especially with respiratory failure or
sepsis
- Renal failure
- Cardiac contusion, or other trauma including surgery, ablation,
pacing, etc
- Aortic dissection
- Aortic valve disease
- Hypertrophic cardiomyopathy
- Tachy- or bradyarrhythmias, or heart block
- Acute neurological disease, including stroke or subarachnoid
haemorrhage
- Apical ballooning syndrome
- Drug toxicity or toxins
- Burns, especially if affecting >30% of body surface
area
- Extreme exertion
References:
- Thygesen K et al Universal definition of myocardial
infarction. Eur Heart J 2007;28:2525
- Jaffe AS, Babuin L, Apple FS.Biomarkers in acute cardiac
disease. J Am Coll Cardiol 2006;48:1"11
- French JK, White HD.Clinical implications of the new definition
of myocardial infarction. Heart 2004;90:99"106
