The definition of those considered to be at sufficiently high risk to benefit from screening varies according to different guidelines. Initially high-risk included people age 55–74 who have smoked a pack of cigarettes daily for 30 years including time within the past 15 years. The United States Preventative Services Task Force (USPSTF) and Centers for Medicare and Medicaid Services (CMS) categorizations are for those age 55–80 and 55-77 respectively who have smoked an average of a pack of cigarettes daily for 30 years and are current smokers or have quit within the past 15 years.