What Causes Elevated CEA Levels?

Before my two lung surgeries my cea level was 11. After second surgery cea was 3.5 six months later it 3.9 six months later it is 4.1. I have smoked for about 40 yrs. Have not smoked for the last 5 yrs. What is your opinion of my cea rising. Should I be considered a smoker and have a 5 or under cea I am 69 yr. old