The ratio is useful if it helps you and your doctor keep the entire picture of your LDL and HDL levels in mind, but it should not take the place of knowing your separate LDL and HDL levels.
Smoking has several harmful effects on cholesterol.
In addition, smoking has harmful effects on the heart and blood vessels. In these ways, smoking substantially raises the risk for coronary heart disease if you are healthy and multiplies that risk many more times if you have other risk factors such as high blood cholesterol. All in all, smoking is the leading preventable cause of death. The more you smoke, the lower your HDL cholesterol is likely to be. Lose weight if you're overweight.