A nurse in an emergency department is caring for a client who reports substernal chest pain and dyspnea. The client is vomiting and is diaphoretic. Which of the following laboratory tests are used to diagnose a myocardial infarction? (Select all that apply)

Rationale: A. LDL cholesterol levels are used to assess a patient’s long-term risk for atherosclerosis and cardiovascular disease, but they do not rise acutely during myocardial infarction and therefore are not useful for diagnosing an MI in the emergency setting. B. Myoglobin is a small heme protein released rapidly from damaged cardiac and skeletal muscle. It can appear in the blood within 1–4 hours after myocardial injury, making it useful for early detection of myocardial infarction. However, it is not specific to cardiac muscle, so elevations could also occur with skeletal muscle injury. Myoglobin is often used in conjunction with other cardiac biomarkers. C. Blood urea nitrogen reflects renal function and may increase in kidney disease or dehydration, but it does not indicate myocardial injury and is not part of the standard diagnostic workup for acute MI. D. Troponin I and T are structural proteins of cardiac muscle, and their levels rise within 3–6 hours after myocardial injury and remain elevated for up to 10–14 days. They are highly sensitive and specific for cardiac injury, making troponin the gold standard for confirming myocardial infarction. E. Creatinine measures kidney function and may be monitored in patients receiving contrast dye or nephrotoxic drugs, but it does not aid in diagnosing an acute MI.