This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pathology
Creatinine kinase is elevated in MI after 
Select and explain. 
A. 2-4hrs, B. 4-8hrs., C. 12-24hrs, D. >24hrs.
A: 2-4hrs
Answer: A: 2-4hrs 
Explanation: CK-MB remains a valuable marker of myocardial injury, second only to the cardiac-specific troponins . Total CK activity is not a reliable marker of cardiac injury since various isoforms of CK are also found in brain, myocardium, and skeletal muscle. However, the CK-MB isoform--principally derived from myocardium, but also present at low levels in skeletal muscle--is the more specific indicator of hea damage. CK-MB activity begins to rise within 2 to 4 hours of MI, peaks at 24 to 48 hours, and returns to normal within approximately 72 hours. (Robbins Basic pathology,9th edition.pg no.382)