Cardiac Troponin Assays

Many clinical chemistry laboratories perform troponin testing to aid in the diagnosis of acute coronary syndrome (ACS). Laboratories must interact with clinicians to establish diagnostic cut points, achieve acceptable assay performance, and troubleshoot questionable findings. Here we present 3 hypothetical scenarios related to troponin testing in the clinical chemistry laboratory.Case Presentation 1: J.P. is an obese 55-year-old male with a history of gastroesophageal reflux disease who presents to the emergency department with substernal chest pain that he attributes to a “large meal.” J.P. is pale and diaphoretic. An ECG shows tachycardia with normal sinus rhythm. J.P.’s troponin levels (decision limit >0.04 μg/L) at presentation and at 6 and 12 hours after presentation are 0.09, 4.41, and 19.62 μg/L, respectively.Cardiac troponin (cTn) has established itself firmly as the “gold standard” in the diagnosis of ACS. cTn should be measured in all patients presenting with symptoms suggestive of ACS, in conjunction with physical examination and ECG.1 Because of the specificity of cTn for myocardial damage, a single cTn above the decision limit, along with clinical evidence, is indicative of myocardial injury. However, serial testing can be useful, depending on clinical presentation and onset of symptoms.cTn is a protein complex, located along the thin filaments of myofibrils, that regulates the contraction of cardiac muscle. It is composed of 3 distinct gene products. cTnC binds calcium, cTnT attaches to tropomyosin on thin filaments, and cTnI inhibits actomyosin ATPase. Expression of each subunit is cardiac restricted. The cardiac isoforms of cTnI and cTnT have additional unique N-terminal amino acid sequences, which allows for specific antibody and assay development and detection of each component in the bloodstream. The diagnostic utilities of cTnI and cTnT are comparable. Most cTn assays are sandwich immunoassays that use either monoclonal or polyclonal antibodies. It is essential …