- Red or tiger top tube
- 5-7 mL of venous blood
Additional information
- Serial sampling is preferred at 0, 6, and 12 hrs after onset of chest pain
- Record date and time of each sample
- Send to lab immediately
Overview of Cardiac Enzymes
- Cardiac troponins (T and I) are specific markers of myocardial damage.
- Each medical facility usually utilizes one of these troponins (T or I) in conjunction with CK and CK-MB testing as part of their cardiac enzyme order set.
- It is typical to order a baseline, 6 hr and 12 hr level of a cardiac specific troponin, CK and CK-MB.
Information on Troponin I testing
- The troponin I (cTnI) test measures the concentration of cardiac troponin I subtype in the blood.
- Troponins are a complex group of three contractile proteins (C, T and, I) which regulate the interaction of actin and myosin in cardiac and skeletal muscle.
- Though structurally the cardiac and skeletal subforms of Troponin C are identical, Troponin T and I have distinct cardiac and skeletal subforms which can be identified by specific assay. Hence Troponin I and T are highly cardiospecific.
- Approximately 2% of cTnI and 6% of cTnT are free in the myocardial cytoplasm.
- Myocardial injury or necrosis results in release of cardiac troponins into the bloodstream as early as 2-6 hrs.
- Troponin I is typically positive within 2-6 hours after cardiac injury and returns to baseline within 7-12 days.
- Troponin I shows a biphasic peak with initial peak at 15-24 hours and then a second lower peak at 60-80 hours.
- cTnI can be analyzed by both qualitative (bedside, point of care) and quantitative assays.
The clinical utility of the serum troponin I test includes:
- Detects myocardial injury (hours after it has occurred)
- Used in the evaluation and diagnosis of chest pain
- Aids in the diagnosis of acute myocardial infarction (AMI) & acute coronary syndrome (ACS)
- Is a sensitive marker for unstable angina
- For detection of perfusion following thrombolysis
- As a prognostic marker and for risk stratification in acute coronary syndromes (ACS)
- To monitor for perioperative myocardial infarction
- For diagnosis of cardiac contusion
- For excluding cardiac injury during electroconversion
- As a biomarker in drug induced cardiotoxicity
- Found to be a prognostic indicator of mortality risk in patients with acute decompensated heart failure (a positive result – 8% mortality versus 2.7% mortality in patients with a negative result)
Advantages of cardiac troponin I test include:
- Better specificity and sensitivity for cardiac damage than CK-MB
- Aids in the early detection of small myocardial infarcts that are undetectable by conventional diagnostic methods
- Detects cardiac damage that has occurred up to 7-12 days prior, since it remains elevated for 7-12 days after injury
- cTnI is more sensitive for the diagnosis of acute myocardial infarction than creatinine phosphokinase MB fraction (CK-MB), myoglobin and lactate dehydrogenase (LDH) isoenzymes
Additional information
- Myocardial injury or necrosis results in release of cardiac troponins into the bloodstream as early as 2-6 hrs.
- Troponin I is typically positive within 2-6 hours after cardiac injury and returns to baseline within 7-12 days.
- Troponin I shows a biphasic peak with initial peak at 15-24 hours and then a second lower peak at 60-80 hours.
- Cardiac troponins are ideal biomarkers for evaluation of ACS in patients with coexistent skeletal muscle injury
- Cardiac troponins have the disadvantage of not being as useful for monitoring for reinfarction due to their prolonged elevation following myocardial injury (one should utilize CK-MB for this purpose)
- Presence of anti-cTnI antibodies can cause false negative test results
- Related laboratory tests include:
- Apolipoprotein A and B
- Aspartate aminotransferase
- Atrial natriuretic peptide
- Blood gases
- B-type natriuretic peptide
- C-reactive protein
- Creatine kinase and isoenzymes
- Electrolytes
- Lactate dehydrogenase and isoenzymes
- Lipid profile
- Lipoprotein electrophoresis
- Myoglobin
- Troponin T
Consult your laboratory for their normal ranges as these will probably vary somewhat from the ones listed below.
| Conv. Units (ng/mL) | SI Units (µg/L) | |
|---|---|---|
| Normal | <0.4 | <0.4 |
| Suggestive of cardiac injury | >1.5 | >1.5 |
Conditions associated with elevated cTnI values include:
- Acute myocardial infarction (AMI)
- Acute coronary syndrome (ACS) or unstable angina
- Myocardial damage after:
- Coronary artery bypass graft surgery
- Other cardiac procedures
- Percutaneous transluminal coronary angioplasty (PTCA)
- Cardiac contusion or trauma
- Cardiac amyloidosis
- Defibrillation
- Nonischemic dilated or hypertrophic cardiomyopathy
- Myocarditis
- Radiofrequency ablation
- Non-cardiac causes:
- Critical illness such as sepsis
- Primary pulmonary hypertension
- Pulmonary embolism
- Scorpion envenomation
- Stroke (especially SAH)
- Very heavy exercise as in marathon
- Cardiotoxic drugs
- b-Sympathomimetics
- Anthracyclines
- Antineoplastics
- Doxorubicin
- Adamcova M et al. Troponin as a marker of myocardiac damage in drug-induced cardiotoxicity. Expert Opine Drug Saf. 2005 May;4(3):457-72.
- Amorim S et al. Troponin I as a marker of right ventricular dysfunction and severity of pulmonary embolism. Rev Port Cardiol. 2006 Feb;25(2):181-6.
- Cantwell RV et al. Cardiac amyloidosis presenting with elevations of cardiac troponin I and angina pectoris. Clin Cardiol. 2002 Jan;25(1):33-7.
- Clark M et al. Elevated cardiac troponins: their significance in acute coronary syndrome and noncardiac conditions. K OklaState Med Assoc. 2006 Jun;99(6):363-7.
- Ebell MH et al. A systematic review of troponin T and I values as a prognostic tool for patients with chest pain. J Fam Pract. 2000 Aug;49(8):746-53.
- Hillis GS et al. The relative utility of cardiac troponin I, creatine kinase-MBmass, and myosin light chain-1 in the long-term risk stratification of patients with chest pain. Clin Cardiol. 2003 Mar;26(3):147-52.
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