Chemistry
Cardiac related
Troponins (Cardiac-specific Troponin I and Troponin T)

Author: Larry Bernstein, M.D. (see Authors page)

Revised: 2 February 2016, last major update March 2011

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Troponins [title] cardiac
Cite this page: Troponins (cardiac-specific Troponin I and Troponin T). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/chemistrycardiactroponins.html. Accessed December 4th, 2016.
Definition / General
Pathophysiology
  • Troponin is a complex of three regulatory proteins that is integral to muscle contraction in skeletal and cardiac muscle, but not smooth muscle
  • Troponin is attached to the protein tropomyosin and lies within the groove between actin filaments in muscle tissue
  • In relaxed muscle, tropomyosin blocks the attachment site for the myosin crossbridge, thus preventing contraction
  • When the muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic reticulum and release calcium into the sarcoplasm
  • Some of this calcium attaches to troponin, causing a conformational change that moves tropomyosin out of the way so that the cross bridges can attach to actin and produce muscle contraction
Clinical Features
  • When heart muscle is damaged, as in myocardial infarction (MI), troponin I and troponin T leak out of cells and into the bloodstream; increased troponin levels indicate cardiomyocyte damage
  • Troponins are not normally present in serum, so any amount present in serum (measured at the 99th percentile of the upper limit of normal at a 10% imprecision) indicates structural damage to the heart, although not necessarily AMI
  • Use of the 99th percentile of the upper limit of normal for diagnosis still requires either typical chest pain or ECG changes of ST depression or T-wave inversion
Laboratory
Test methodology
  • Numerous diagnostic companies make troponin I immunoassays available on different platforms

Test indications
  • Typical or atypical chest pain, or ECG changes suspicious for non Q-wave AMI
  • These may be combined with risk factors for AMI

Test limitations
  • Both troponin I (TnI) and troponin T (TnT) are affected by renal insufficiency, but TnT is to a greater extent
  • 100% of TnT is excreted in urine, but 70% of TnI is degraded by vascular endothelium
    • This means that minor elevations of troponins have to be considered in the context of comorbidities, especially renal impairment, and risk factors
  • Among heart failure patients, the objective parameter of NT-proBNP seems more useful to delineate the "cardiorenal syndrome" than the previous criteria of a clinical diagnosis of heart failure

Reference ranges
  • TnI: < 0.3 ng/ml
  • TnT: < 0.03 ng/ml

High values
  • Suspect AMI for TnI above 0.7 ng/ml or for TnT at 0.07 ng/ml or higher
  • Minor elevations above the defined upper limit of normal may be due to impaired renal clearance, or indicate a cardiac structural change that requires further investigation