This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
Patient is having normal CK & CKMB after 2 days of chest pain which of the following is true- 
Select and explain. 
A. Excludes diagnosis of MI, B. Reperfusion after MI, C. Extracardiac source of pain, D. Cardiac surgery
A: Excludes diagnosis of MI
Answer: A: Excludes diagnosis of MI 
Explanation: A significant concentration of CK-MB isoenzyme is found almost exclusively in the myocardium, and the appearance of elevated CK-MB levels in serum is highly specific and sensitive for myocardial cell wall injury. Normal reference values for serum CK-MB range from 3 to 5% (percentage of total CK) or 5 to 25 IU/L.if theses are normal then the MI diagnosis can be excluded Ref Davidson edition23rd pg 440