Biochemical investigations for myocardial infarction
The use of traditional cardiac enzymes for the diagnosis of AMI/ACS (myocardial infarction / acute coronary syndrome) has now been replaced by the use of troponin. The cardiac troponins are specific for cardiac damage and their presence in blood in the clinical scenario of chest pain is now considered diagnostic of ischaemic cardiac damage. There is a rise and fall in cardiac troponin after ischaemic damage and if the blood sample is taken at the wrong time a low values or false negative will be seen.
It should be noted that cardiac troponins are raised in ALL forms of myocardial damage and do not indicate ischaemic damage by themselves. It should also be noted that stress and strain on the heart eg heart failure or right sided strain with pneumonia or pulmonary embolus also results in raised cardiac troponin (see table below).
The LTH laboratoruies use the Ultra-troponin I (Siemens Centaur method) which has a 99th centile value of 50 ng/L (diagnostic value for ACS in appropriate clinical context). It should be noted that there are many troponin I assays in use in the world and that they do NOT all have the same decision value.
See also section on Lipids.
Non-ACS causes of raised troponin
- Acute and chronic heart failure
- Hypertension and hypotension
- Renal failure
- Critical illness
- Pulmonary embolus
- Burns esp if TBSA > 30%
- Acute neurological disease inc CVA