History/Background and/or General Information
Troponin is a muscle protein that attaches to both actin and tropomyosin. It is concerned with calcium binding and inhibiting cross-bridge formation. Troponin is a complex of three proteins: troponin C, troponin I, and troponin T. The distribution of these isoforms varies between cardiac muscle and slow- and fast-twitch skeletal muscle. Their importance lies in the fact that the isoforms troponin I and troponin T show a high degree of cardiac specificity, and therefore, have an important role in the diagnostic evaluation of a patient presenting with symptoms suggestive of a cardiac origin.
Cardiac Troponin I (cTnI) is highly specific for myocardial tissue, is thirteen times more abundant in the myocardium than CK-MB on a weight basis, is not detectable in the blood of healthy persons, shows a greater proportional increase above the upper limit of the reference interval in patients with myocardial infarction and remains elevated for seven to ten days after an episode of myocardial necrosis. In addition, measurements of cTnI is useful to clarify which increases in CK-MB are due to myocardial injury and which ones reflect acute or chronic skeletal muscle abnormalities.
Troponin T, the tropomyosin-binding protein of the regulatory complex located on the contractile apparatus of cardiac myocytes, is also a sensitive and specific marker for myocardial necrosis. Damaged heart muscle releases the protein, troponin T, which increases in the bloodstream as early as 3 hours after the onset of chest pain and remains at an elevated level for 2 to 7 days.
Covered Indications
Troponin levels are considered medically reasonable and necessary to rule out myocardial injury only under the following conditions
- patient presents with signs and symptoms of an acute myocardial infarction (prolonged chest pain often described as squeezing, choking, stabbing, etc., usually spreading across chest to the left arm; dyspnea, diaphoresis) which is confirmed by an electrocardiogram (EKG, ECG);
- patient presents with vague or atypical symptoms suggestive of a cardiac origin, which is not confirmed by an electrocardiogram;
- patient evaluation reveals a normal creatine kinase MB isoenzyme (CK-MB), however, the EKG demonstrates new changes consistent with ischemia (e.g., flipped T waves, ST-segment depression); or
- to distinguish patients with unstable angina from those with a non-Q wave myocardial infarction.
Limitations
Initially, it is expected that a qualitative Troponin level is performed on a patient with suspected myocardial injury. If the results of the qualitative Troponin level is positive, then the quantitative level of Troponin I or Troponin T is performed, usually with the same blood specimen, to determine if the symptoms are cardiac in nature. The Troponin C isoform is not useful in the management of myocardial infarction and it is not necessary to monitor both the T and I isoform.
The quantitative test is normally performed every 8-12 hours the first 24 hours. Once the determination is made whether myocardial injury has occurred, it is expected that a Troponin level will be performed only when the results are to be used in the active treatment of the patient.
Also, it is not necessary to use Troponin in addition to Creatine Kinase in the management of patients with myocardial infarction.
As published in the CMS IOM Publication 100-08, Medicare Program Integrity Manual, Chapter 13, Section 13.5.4, an item or service may be covered by a contractor LCD if it is reasonable and necessary under the Social Security Act Section 1862 (a)(1)(A). Contractors shall determine and describe the circumstances under which the item or service is considered reasonable and necessary.
