The World Health Organization principles for population screening state that screening should only be implemented when there is a good balance between costs and benefits.[1
] Unfortunately there is no universal definition for “good balance” and different institutions may have different assessments of whether the incremental cost of one intervention over another is warranted by the additional benefits it provides. An intervention that provides an additional year of life at an incremental cost of $50,000 or less is deemed acceptable in most industrialized countries, but thresholds of even $100,000 per life-year gained have been argued to be acceptable in some settings.[5
To ensure efficient use of resources, the incremental cost-effectiveness ratio, not the ratio of each strategy compared to standard of care, should be compared to the threshold cost per (quality-adjusted) life-year gained.[6
] This requirement is illustrated by the following example: a recent US study found that the cost-effectiveness ratio of stool DNA testing for CRC compared with no CRC screening is $13,000–$18,000 per life-year gained.[8
] With this ratio, stool DNA testing would be considered cost-effective even if the decision-maker is only willing to pay $20,000 per life-year gained. One might therefore recommend implementing a stool DNA screening program. However, annual screening with a faecal occult blood test (FOBT) was estimated to save more life-years than stool DNA testing at a lower cost and therefore strongly dominated stool DNA testing. Implementing a stool DNA screening program would therefore lead to higher costs and fewer life-years gained compared with an FOBT screening program.
There is however a situation where the cost-effectiveness ratio compared to no screening could be considered the appropriate measure of cost-effectiveness of a screening test, namely if the test would entice a previously unscreened segment of the population to adhere to screening. For example, less than 60% of the population currently adheres to CRC screening.[9
] Most cited reasons for nonparticipation are practical reasons (e.g., conflicts with work or family, inconvenience, being too busy, lack of interest, and cost) and not having any current health problems or symptoms of CRC.[14
] These barriers exist regardless of the screening test. However, other reasons for nonparticipation are worry about pain, discomfort, or injury associated with the examination or that the test would be embarrassing or unpleasant.[14
] New screening tests such as computed tomographic (CT) colonography, stool DNA tests, and serum tests aim to eliminate (some of) these barriers. If there is good evidence that these tests indeed are able to increase adherence among those who would otherwise remain unscreened, then the cost-effectiveness ratio compared to no screening would be an appropriate measure for decision-making since for these people no screening is the relevant comparator.