Troponin I

Clinical use: In the absence of a myocardial event values will be less than .4ng/ml. At a cut-off limit of .1 ng/ml specificity is 99.5%.
Background: Troponin is a protein complex which regulates the contraction of striated muscle. It consists of three subunits which are located periodically along the thin filament of the myofibrils. Troponin C binds calcium, Troponin T attaches to tropomyosin on the thin filament, and Troponin I inhibits actomyosin ATPase.

Troponin I (TnI), an inhibitory protein of the troponin-tropomyosin complex, exists in three distinct isoforms: cardiac muscle, slow-twitch skeletal muscle, and fast-twitch skeletal muscle. Each isoform is encoded by a distinct gene, each with a unique amino acid sequence, leading to 40% dissimilarity among isoforms. The cardiac form of Troponin I is further unique having 31 additional amino acid residues on its N-terminal, not present in the skeletal forms, which allows for specific polyclonal and monoclonal antibody development.

The cardiac specificity of this isoform improves the accuracy of diagnosis in patients with acute or chronic skeletal muscle injury and possible concomitant myocardial injury, and is the basis for its selection as a cardiac marker in the diagnosis of acute MI.

TnI is the only troponin isotope present in the myocardium and is not expressed during any developmental stage in skeletal muscle. TnI has a molecular weight of 24,000 daltons. Clinical studies have reported that TnI is released into the bloodstream within hours of the onset of symptoms of MI or ischemic damage. It can be detected at 3 to 6 hours following onset of chest pain with peak concentrations at 12 to 16 hours, and remains elevated for 5 to 9 days, providing more opportunity for detecting MI or excluding the diagnosis.

Reference ranges: No reference range reported – please see sample report for more information.
Associated diseases:
Patient preparation:
Specimen requirements: Sample type:

  • Serum is the recommended sample type for this assay, although heparinised plasma may be used.

Sample identification:

  • Three patient identifiers from
    • Name
    • DOB
    • Address
    • NHS number
    • Unit number

    should match on the specimen and request form. This check may be performed prior to centrifugation by the Central Sort department.

Turnaround time: 2 hours
Additional information:
Referred test: