Since lesions can only be detected if follow-up colonoscopy is performed, the definitions below take
into account whether or not follow-up CS was actually performed. Other positive predictive values can
be calculated, such as the PPV of the positive test without any further adjustment. In this case, the
denominator would be the number of people presenting with a positive test result leading to referral
for colonoscopy.
PPV for detection of lesions
The positive predictive value (PPV) for detection
of a lesion through an FOBT screening programme
is defined as the percentage of people with
detection of at least one lesion at follow-up CS
among those with positive FOBT tests who have
attended follow-up CS.
N people with at least one detected lesion
during the time frame *
N people positive to FOBT having attended a
colonoscopy during the time frame*
* equal to the defined screening interval or
reporting period
PPV for detection of adenoma
The positive predictive value for detection of an
adenoma through an FOBT screening programme
is defined as the percentage of people with
detection of at least one adenoma at follow-up CS
among those with positive FOBT tests who have
attended follow-up CS.
N people with at least one detected
adenoma during time frame*
N people positive to FOBT having attended a
colonoscopy during the time frame*
* equal to the defined screening interval or
reporting period
