Troponin
Troponin is a protein of muscle, blood levels of which have become important in diagnosis. "Its function is to serve as the calcium-binding component in the troponin-tropomyosin B-actin-myosin complex by conferring calcium sensitivity to the cross-linked actin and myosin filaments.[1]
"Cardiac troponins are regulatory proteins of the thin actin filaments of the cardiac muscle. Troponin T and troponin I are highly sensitive and specific markers of myocardial injury."[2] The level of troponin in the blood of normal individuals may be less than 0.0064 microg/l according to a study of a highly sensitive assay.[3] However, even this cutoff level does not perfectly discriminate normal individuals from patients having acute coronary syndrome.
Troponin levels have become an important diagnostic tool in assessing acute coronary syndrome, but it is dangerous to assume that ACS is the only reason they may be elevated. They supplement, but do not replace, the electrocardiogram, history, and physical examination.
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Test accuracy
Myocardial infarction
Clinical practice guidelines jointly written by multiple expert groups anchor the diagnosis of myocardial infarction on troponin blood assays obtained within 6 hours and again within 8-12 hours of a patient arriving for medical care.[4]
In NSTEMI, typical troponin I levels are less than 9 ng/ml with the median values 1.0 to 2.0 nl/ml.[5]
Accuracy for detecting myocardial infarction is improved by using a high sensitivity assay.[6] A more recent study using highly sensitive and contemporary troponin I suggests testing for either assay upon arrival and at three hours. If either the initial or value at 3 hours is abnormal, an infarction is suspected.[7]
Chronic stable coronary heart disease
The highly sensitive assay can detect elevations in patients with chronic stable coronary heart disease.[8] These patients are at increased risk of adverse events.[8]
References
- ↑ Anonymous (2024), Troponin (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Ammann P et al.' (2004 May 1), "Raised cardiac troponins: Causes extend beyond acute coronary syndromes", BMJ 328 (7447): 1028–1029., DOI:10.1136/bmj.328.7447.1028
- ↑ Venge P, Johnston N, Lindahl B, James S (2009). "Normal plasma levels of cardiac troponin I measured by the high-sensitivity cardiac troponin I access prototype assay and the impact on the diagnosis of myocardial ischemia.". J Am Coll Cardiol 54 (13): 1165-72. DOI:10.1016/j.jacc.2009.05.051. PMID 19761938. Research Blogging.
- ↑ Anderson JL, Adams CD, Antman EM, et al (2007). "ACC/AHA 2007 guidelines for the management of patients with unstable angina/non-ST-Elevation myocardial infarction: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 2002 Guidelines for the Management of Patients With Unstable Angina/Non-ST-Elevation Myocardial Infarction) developed in collaboration with the American College of Emergency Physicians, the Society for Cardiovascular Angiography and Interventions, and the Society of Thoracic Surgeons endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation and the Society for Academic Emergency Medicine". J. Am. Coll. Cardiol. 50 (7): e1–e157. DOI:10.1016/j.jacc.2007.02.01. PMID 17692738. Research Blogging.
- ↑ Antman EM, Tanasijevic MJ, Thompson B, Schactman M, McCabe CH, Cannon CP et al. (1996). "Cardiac-specific troponin I levels to predict the risk of mortality in patients with acute coronary syndromes.". N Engl J Med 335 (18): 1342-9. DOI:10.1056/NEJM199610313351802. PMID 8857017. Research Blogging.
- ↑ Reichlin T, Hochholzer W, Bassetti S, Steuer S, Stelzig C, Hartwiger S et al. (2009). "Early diagnosis of myocardial infarction with sensitive cardiac troponin assays.". N Engl J Med 361 (9): 858-67. DOI:10.1056/NEJMoa0900428. PMID 19710484. Research Blogging.
- ↑ Keller T, Zeller T, Ojeda F, Tzikas S, Lillpopp L, Sinning C et al. (2011). "Serial changes in highly sensitive troponin I assay and early diagnosis of myocardial infarction.". JAMA 306 (24): 2684-93. DOI:10.1001/jama.2011.1896. PMID 22203537. Research Blogging.
- ↑ 8.0 8.1 Omland T, de Lemos JA, Sabatine MS, Christophi CA, Rice MM, Jablonski KA et al. (2009). "A Sensitive Cardiac Troponin T Assay in Stable Coronary Artery Disease.". N Engl J Med. DOI:10.1056/NEJMoa0805299. PMID 19940289. Research Blogging.