Final answer:
Increased troponin levels are diagnostic of a myocardial infarction, and this is a highly specific indicator for heart muscle damage occurring during an MI.
Step-by-step explanation:
A nurse caring for a client who had an onset of chest pain 25 hours ago should identify that the increase in troponin levels is diagnostic of myocardial infarction (MI). Cardiac troponin is a regulatory protein for muscle contraction that is released into the blood when the heart muscle is damaged. Elevated troponin levels are considered a highly specific indicator for an MI. Other blood tests that can indicate MI include creatine kinase MB (CK-MB) and lactate dehydrogenase (LDH), but troponin remains the most reliable marker, particularly within the first few hours to days following an onset of chest pain.