For high sensitivity TNI assay used at MMC Marshfield lab:
Serial measurements may be necessary to confirm or exclude the diagnosis of acute coronary syndrome. Repeat testing in 2 hours if clinically indicated.
-If zero hour TNI is <8 ng/L AND delta at two hours is < 7 ng/L, then rule out Acute MI.
-If zero hour TNI is >=120 ng/L OR delta at two hours is >=20 ng/L, then rule in Acute MI.
-If results do not fall into above, then observe. Getting additional draws (e.g. at 4 hours) may be helpful.
For all other sites reporting TNI:
The 99th percentile URL for troponin I in a normal reference population is approximately 45 ng/L.
Values >45 ng/L are consistent with myocardial injury.
Serial measurements may be necessary to confirm or exclude the diagnosis of acute coronary syndrome.
Repeat testing in 3 to 6 hours if clinically indicated.
Cardiac Troponin I (cTnI) is very specific to myocardium and not expressed during any developmental stage in skeletal muscle. Increased levels of cTnI are detected with myocardial injury. Detection of rise and/or fall of cTnI are essential to establish the diagnosis of acute myocardial infarction (MI). An increased cTnI concentration is defined as a value exceeding the upper reference limit of the 99th percentile of a normal reference population and is designated as the decision limit for the diagnosis of acute MI (Third Universal definition of Myocardial infarction, ESC/ACCF/AHA/WHF Expert consensus document. Circulation 2012; 126: 2020). Demonstration of rising and/or falling pattern is required to distinguish acute from elevations of cTnI levels that are associated with chronic heart diseases.
A positive cTnI result therefore, is not always indicative of ischemia. Other conditions resulting in myocardial cell damage can contribute to elevated cTnI include, but are not limited to:
Elevated Tnl Values in Patients Without AMI
Cardiac conditions
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Angina/Unstable Angina
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Atrial fibrillation
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Cardiac surgery
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Cardiomyopathy
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Congestive heart failure
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Coronary artery disease
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Heart failure
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Hypertensive urgency
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Myocarditis
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Pericarditis
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Pulmonary emoblism
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Recent cardiac intervention
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Severe valvular heart disease
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Tachycardia
Non-cardiac conditions
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Chronic lung disease
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Cardiac contusion related to a traumatic injury
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Renal failure
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Pneumonia
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Pulmonary embolism
For assessing acute MI, blood samples should be drawn at the time of admission and repeated at 3 to 6 hours intervals. On certain occasions additional samples between 12 and 24 hours may be required if earlier measurements are not elevated and clinical suspicion is high for MI.