Number needed to screen for colorectal cancer mortality by age groups with varying underlying baseline risk11
| Screening test | Age group, yr | Absolute risk reduction, %* | NNS (95% CI) |
|---|---|---|---|
| Biennial gFOBT | < 60 (45–59) | 0.0377 | 2655 (1757–6244) |
| Biennial gFOBT | ≥ 60 (60–80) | 0.2032 | 492 (326–1157) |
| Flexible sigmoidoscopy | < 60 (45–59) | 0.0540 | 1853 (1441–2713) |
| Flexible sigmoidoscopy | ≥ 60 (60–80) | 0.2912 | 343 (267–503) |
Note: CI = confidence interval, gFOBT = guaiac fecal occult blood testing, NNS = number needed to screen, RR = relative risk.
↵* The estimates of absolute risk reduction in colorectal cancer mortality for screening versus control and NNS to prevent one death from colorectal cancer are based on age-specific baseline risk of dying from colorectal cancer (obtained from SEER Cancer Statistics Review, 1975–2012,21 the RR reduction (obtained from pooled estimate for colorectal cancer mortality for biennial gFOBT [RR reduction 0.8215; 95% CI 0.7303–0.9241] and flexible sigmoidoscopy screening [RR reduction 0.7442; 95% CI 0.6710–0.8253]) and the life expectancy over which the patient is expected to be screened.11