A common scenario in the preoperative evaluation of an acutely ill patient is the discovery of a positive troponin. Although this is commonly interpreted as a sign of myocardial ischemia, this may or may not be the case. Positive troponins occur without myocardial infarction (MI) in several situations that have implications for perioperative care very different than those of active MI.

Troponins I, T, and C form a complex with actin and myosin and control contraction in cardiac and skeletal muscle. A small amount of cardiac troponin is cytoplasmic, whereas the rest is sarcomeric. Although cardiac and skeletal muscle share isoforms of troponin C, cardiac troponins I and T are distinct from skeletal isoforms.

Since the year 2000, the international consensus definition of MI has included positive troponins with gradual rise and fall, and clinical evidence of MI (characteristic electrocardiogram changes or ischemic symptoms). Within 3 years of the introduction of this definition, the incidence of emergency department-diagnosed acute MI increased nearly 200%. Clearly, troponin values are a sensitive tool with which to diagnose myocardial ischemia, but this sensitivity has posed some problems. The value of this test led to the marketing of a large number of diagnostic assays, which have improved significantly since their introduction; early assays were less specific for cardiac troponins. The variety of assays means that clinical labs at different institutions must promulgate their own norms; values must be interpreted relative to the local reference values. It is not unheard of for neighboring institutions to have upper-limit-of-normal values that differ by an order of magnitude.

The earlier, nonspecific assays created confusion when emergency departments began using them in patients with low pretest probability of MI. What appeared to be spurious positives were found to be quite common. Although the newer assays are more specific, there are still disease states other than acute MI that can elevate blood levels of cardiac troponins T and I. Familiarity with these states can prevent embarrassing mistakes, complications, and unnecessary case cancellations.