Positive predictive values for FOBT screening programmes

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 

 PPV for detection of advanced adenoma 

The positive predictive value for detection of an advanced adenoma through an FOBT screening programme is defined as the percentage of people with detection of at least one advanced adenoma at follow-up CS among those with positive FOBT tests who have attended follow-up CS. Values varied between 14.6% and 54.5% in the RCTs using only gFOBT without rehydration and from 6.0% to 11.0% with rehydration.  

N people with at least one detected advanced adenoma advanced 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 

 PPV for detection of cancer  

The positive predictive value for detection of a cancer through an FOBT screening programme is defined as the percentage of people with detection of at least one cancer at follow-up CS among those with positive FOBT tests who have attended follow-up CS. Values varied between 5.2% and 18.7% in the RCTs without rehydration and from 4.5% to 8.6% in the initial round of population-based programmes (5.3% to 10.6% in subsequent screening)

N people with at least one detected cancer 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  

Endoscopic complications in FOBT screening programme 

For any complication the rate is defined as the proportion of participants presenting with a complication among those having attended a colonoscopy during the respective time frame. The rate should be calculated in total and separately for screening and follow-up colonoscopy if applicable.

N people presenting with complication during the time frame* 

N people having attended a colonoscopy during the time frame * 

* equal to the defined screening interval or reporting period