The nurse is admitting a patient suspected of having an acute myocardial infarction. The physician orders lab tests to confirm the diagnosis. An increase in the isoform of creatine kinase (CK-MB) is expected how soon after the onset of chest pain?
• Serum CK-MB levels start to elevate 4 to 6 hours after the onset of chest pain. Levels usually peak around 12 to 18 hours after onset of chest pain, then return to normal after 48-72 hours.
• CK-MB is expressed mainly in heart muscle. Levels can rise following an infarction, but its elevation has a short duration, so its use is appropriate for acute presentation of recent heart damage.
• There is a small amount of CK-MB present in skeletal muscle, but if skeletal muscle damage is not present, it is a relatively good indicator of heart damage. If there is skeletal muscle damage (from a multivessel intervention (MVI), for example), this test would not be used to detect a heart attack.