Study type: Blood. The laboratory should be contacted prior to specimen collection to determine the appropriate collection container. Collection requirements vary between different testing methods. Generally, green-top [heparin] tubes are required for (HScTnT), while some troponin I tests may be run on either plasma collected in a green-top [heparin] or lavender-top [EDTA] tube or run on serum collected in red/gray or red-top tube; related body system: Circulatory system. Care must be taken to use the same type of collection container if serial measurements are to be taken. It should also be noted that values obtained from different assays do not correlate, e.g., rapid point-of-care screen performed in the emergency department will not compare to the main laboratory’s automated assay.

Cardiovascular disease remains one of the leading causes of death in the United States. Troponin, considered the gold standard for diagnosing acute MI, is the preferred and sometimes sole cardiac marker used when a patient initially presents for evaluation of suspected MI. Troponin is a complex of three contractile proteins that regulate the interaction of actin and myosin. Troponin C is the calcium-binding subunit; it does not have a cardiac muscle–specific subunit. Troponin I and troponin T, however, do have cardiac muscle–specific subunits with separate and unique functions.

High-sensitivity cardiac troponin I (HScTnI) and high-sensitivity cardiac troponin T (HScTnT) assays have been approved by the U.S. Food and Drug Administration, and many laboratories have begun using the newer technology. While the high-sensitivity assays detect the presence of troponin sooner than the traditional methods, there is variability between the different test methods in cutoff values, sensitivity, and specificity of the protein segments or troponin epitopes being measured. These variations, as well as considerations regarding interpretation of results, require collaboration between assay manufacturers, laboratorians, and health-care providers during the process of evaluating and implementing high-sensitivity troponin assays.

Troponin I is only found in myocardial muscle tissue and is therefore thought to be a more specific marker of cardiac damage than troponin T. Cardiac troponin I begins to rise 3 to 6 hr after onset of chest pain accompanying MI, peaks between 12 and 16 hr, and resolves in 5 to 9 days.

Troponin T is present in the intracellular fluid of both striated cardiac and striated skeletal muscle cells and is therefore not considered as specific as cTnI for identifying MI. Levels of cTnT rise faster than cTnI and are detectable between 2 and 4 hr after MI, may peak somewhat later, and remain elevated longer (14 days or more).

Guidelines vary widely for concurrent serial testing of other cardiac markers including CK-MB. Multiple measurements of CK-MB may be used to identify cardiac injury subsequent to the initial infarct because unlike the release of CK-MB, once the troponin is increased to the point of being diagnostic for MI, further myocardial injury does not produce a new spike in troponin levels. Serial CK-MB measurements may also be used to rule out MI in the instance where the cTnT level is somewhat elevated related to a false positive caused by damage to striated skeletal muscle from other causes.

For additional information regarding screening guidelines for atherosclerotic cardiovascular disease (ASCVD), refer to the study titled “Cholesterol, Total and Fractions.”