Final answer:
Following an MI, troponin levels are elevated first and are considered a primary marker for diagnosis, followed by creatine kinase MB.
Step-by-step explanation:
The labs that are elevated first following an myocardial infarction (MI) are the cardiac biomarkers, including troponin levels and creatine kinase MB (CK-MB). Of these, troponin is a highly specific and sensitive marker that becomes elevated within a few hours post-MI and remains elevated for a prolonged period. Creatine kinase MB also gets elevated following MI but troponin is usually considered the primary marker for the diagnosis of an MI.