Estimates of the sensitivity of screening sigmoidoscopy assume an adequate depth of insertion is reached. However, in clinical practice, the frequency that sigmoidoscopy reaches various lengths of the colon is not known. We assessed the frequency of inadequate reach (depth of <50 cm of the colon) in a large U.S. cohort, according to age and sex.

We performed a cross-sectional study of 15,406 asymptomatic persons aged 50 years or older who underwent screening flexible sigmoidoscopy between April 1997 and October 2001 at sites participating in the Clinical Outcomes Research Initiative, which examines outcomes of endoscopy in “real life” settings. The maximum depth of insertion of the sigmoidoscope was measured in centimeters from the anus and classified as adequate (≥50 cm) or inadequate (< 50 cm). Patient characteristics as well as procedure-related variables were also recorded.

Eighteen percent (n = 2801) of subjects had an inadequate examination. In men, the percentage of inadequate examinations increased progressively with age, from 10% (343/3338) in those aged 50 to 59 years to 22% (53/248) in those aged 80 years or older (P <0.001). Inadequate examinations were more common in women at all ages, ranging from 19% (733/3798) in those aged 50 to 59 years to 32% (86/267) in those aged 80 years or older (P <0.001). These associations were confirmed in a multivariable analysis.

Our finding that advancing age and female sex were independently associated with the risk of inadequate reach of screening sigmoidoscopy suggests that the sensitivity of sigmoidoscopy may be lower in these populations. Estimates of the benefits of sigmoidoscopy may need to be tailored to the age and sex of the patient.