The ACCF 2012 Expert Consensus Document is helpful.
Points of interest:
MI type designations 1-5, respectively, denote unstable coronary artery obstruction, demand ischemia (supply/demand imbalance), sudden unexpected cardiac death, association with PCI and association with CABG. Though all are considered MI only type 1 is considered ACS.
In other situations troponin elevations signify myocardial involvement but not MI such as stroke, PE, sepsis, heart failure (see here) and chest trauma.
Some cases are non cardiac and due to lab artifacts or interfering substances (e.g. heterophile antibodies).
Consider the pretest probability and apply bayesian reasoning in unclear cases.
A CKMb is useful for confirmation in some cases.