UNDERSTANDING TROPONINS: HOW IMPORTANT IT IS
Troponins (TnT & CTnI) as cardiac biomarkers found to be superior to creatinine Kinase – MB (CK – MB) as indicators of myocardial damage.1 They have proven to be useful in diagnosis and risk satisfaction of patients presenting with acute chest pain in emergency room.2 Troponins are released as a result of myocardial damage regardless of etiology. Other than ischemia there are myriad conditions that may cause elevation of troponin levels.
Normal findings mentioned in the literature are cardiac troponins T:<0.1ng/ml, cardiac troponin I:<0.03ng/ml & high sensitivity troponin T<14ng/l for women & <22ng/l for men.3
There is a difference in the rise and fall pattern with old generation and modern assays. With the older generation assays elevated troponin levels can be detected 6-12 hours after onset of myocardial injury peaking at 24 hours with a decline up to 2 weeks. With modern assays elevation is detected in 3-4 hours after onset of myocardial injury. Its recommended to recheck troponins at 6-12 hours and up to 24 hours after symptoms onset2 & Non-ST segment myocardial infection can be detected earlier i.e. at 3-4 hours after symptoms onset.4
The important point clinician should be aware is to know abnormal reference range for the assays used in practice, causes of troponin elevation other than myocardial infarction.5- 9
Next important step is collection of blood sample for troponins. It is collected as whole blood through venipuncture. No fasting and no special preparation are needed and can be collected at any time of the day. Troponin T requires heparinized test tubes while EDTA or heparinized tubes for troponin.10,11 The turnaround time for troponin measurement in setting of chest pain should be 60 minutes and all laboratories to achieve this time.12
In patients with borderline elevation of troponins need for seminal testing is important. The initial recommendations were to check the markers every 6 hours until expected peak was reached. Now more sensitive assays are available and very low concentration of elevated cardiac markers can be detected and evidence has demonstrated that checking troponins 3-4 hours after initial draw can help in early diagnosis.13 Last but not the least analytical factors that may lead to falsely elevated troponins results include incompletely clotted specimen,14 Heterophile antibodies15 Rheumatoid factor16 elevated bilirubin levels17 immune complex formation18 markedly elevated alkaline Phosphates levels19 and analyzer malfunction.20
In conclusion, levels of troponins should be interpreted in relation to history and ancillary tests. False-positive results should be kept in mind in decision making, if elevated, troponins will provide a visa to take these patients to catheterization laboratory unnecessary.
- Ganongâs Review of Human physiology. 24th edition,. ISBN 978-0-07-178003-2: The McGraw-Hill Companies, Inc.; 2012.
- Morrow DA, Cannon CP, Jesse RL, Newby LK, Ravkilde J, Storrow AB, et al. National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: clinical characteristics and utilization of biochemical markers in acute coronary syndromes. Clin Chem. 2007;53(4):552-74.
- Pagana KD, Pagana TJ, Pagana TN. Mosby's Diagnostic and Laboratory Test Reference, St. Louis, Mo: Elsevier. 2019:600-50.
- Rao V, Cheng Y, Lindert S, Wang D, Oxenford L, McCulloch AD, et al. PKA Phosphorylation of Cardiac Troponin I Modulates Activation and Relaxation Kinetics of Ventricular Myofibrils. Biophys J. 2014;107(5):1196-204.
- Bakshi TK, Choo MK, Edwards CC, Scott AG, Hart HH, Armstrong GP. Causes of elevated troponin I with a normal coronary angiogram. Intern Med J. 2002;32(11):520-5.
- Zellweger MJ, Schaer BA, Cron TA, Pfisterer ME, Osswald S. Elevated troponin levels in absence of coronary artery disease after supraventricular tachycardia. Swiss Med Wkly. 2003;133(31-32):439-41.
- Nunes JP, Garcia JM, Farinha RM, Silva JC, Magalhães D, Pinheiro LV, et al. Cardiac troponin I in aortic valve disease. Int J Cardiol. 2003;89(2-3):281-5.
- Hamwi SM, Sharma AK, Weissman NJ, Goldstein SA, Apple S, Canos DA. Troponin-I elevation in patients with increased left ventricular mass. Am J Cardiol. 2003;92(1):88-90.
- Velmahos GC, Karaiskakis M, Salim A, Toutouzas KG, Murray J, Asensio J. Normal electrocardiography and serum troponin I levels preclude the presence of clinically significant blunt cardiac injury. J Trauma. 2003;54(1):45-50.
- Panteghini M. Recommendations on use of biochemical markers in acute coronary syndrome: IFCC proposals. EJIFCC. 2003;14(2):104-8.
- Keller T, Zeller T, Ojeda F, Tzikas S, Lillpopp L, Sinning C, et al. Serial changes in highly sensitive troponin I assay and early diagnosis of myocardial infarction. JAMA. 2011;306(24):2684-93.
- Certificate of Analysis Standard Reference Material 2921, Human Cardiac Troponin Complex. 2004. National Institute of Standards and Technology. Available at http://www.nist.gov/srm.
- Licka M, Zimmermann R, Zehelein J, Dengler TJ, Katus HA, Kubler W. Troponin T concentrations 72 hours after myocardial infarction as a serological estimate of infarct size. Heart. 2002;87(6):520-4.
- Roongsritong C, Warraich I, Bradley C. Common causes of troponin elevations in the absence of acute myocardial infarction: incidence and clinical significance. Chest. 2004;125(5):1877-84.
- Kazmierczak SC, Sekhon H, Richards C. False-positive troponin I measured with the Abbott AxSYM attributed to fibrin interference. Int J Cardiol. 2005;101(1):27-31.
- Kricka LJ. Kricka LJ. Human Anti-Animal Antibody Interferences in Immunological Assays. Clin Chem. 1999;45(7):942-956.
- Dasgupta A, Banerjee SK, Datta P. False-positive troponin I in the MEIA due to the presence of rheumatoid factors in serum. Elimination of this interference by using a polyclonal antisera against rheumatoid factors. Am J Clin Pathol. 1999;112(6):753-6.
- Hawkins RC. Hemolysis interference in the ortho-clinical diagnostics vitros ECi cTnI assay. Clin Chem. 2003;49(7):1226.
- Plebani M, Mion M, Altinier S, Girotto MA, Baldo G, Zaninotto M. False-positive troponin I attributed to a macrocomplex. Clin Chem. 2002;48(4):677-9.
- Troponin: What Laboratorians Should Know to Manage Elevated Results. Available at http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/TipsandArticlesonDeviceSafety/ucm109362.htm.
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