The Effectiveness of Fecal Immunochemical Tests May Decrease After Repeated Diagnostic Rounds For Colon Cancer

Another great experimental study out of the Netherlands on the effects of the Fecal Immunochemical Test (FIT) after repeated rounds of testing.

Summary: The main objective of the study was to determine the effects of repeated testing using the Fecal Immunochemical Tests (FIT).  Tests such as these can often have low evaluative test measures (high false negatives and positives) so it is important to do repeated testing - especially after an initial positive finding.  The study was conducted in two concurrent stages in order to determine the effectiveness .  Somewhat alarmingly, the Positive Predictive Value (PPV) was found to decrease from the first round to the second round of testing for the FIT test for those patients which had a negative result in the first round.  The PPV is an evaluative measure for a diagnostic test which divides the number of people who actually have the condition by all of those who tested positive for the condition: True Positives/(True Positives+False Positives)).  

Implications for Practice: The fact that the PPV decreased for the Fecal Immunochemical Test should come at somewhat of an alarm for Gastroenterologists. This result just helpsenforce the importance of getting a Colononscopy for patients if there is suspect of any bowel instabilities, as the the other diagnostic tests really can not measure up to a Colonoscopy.  Interestingly, the authors also found that there was no significant difference between a fecal immunochemical test (FIT) and a fecal occult blood test (FOBT: another diagnostic measure).  Thus, there is no reason to switch from a FIT based program to a FOBT based program.

Interestingly, the authors showed that there were several different sub-types of colon cancers which were diagnosed, and this suggests the potential that some sub-types may be more easily detected than others.  Another study did show that the sensitivity of the Fecal Immunochemical Test (FIT) is higher for cancers which are detected distal rather than proximal, and this may have something to do with it.