PWE-282 Implications of a ‘false negative’ faecal occult blood test (FOBT) – results from a multicentre study

Abstract

Introduction We aimed to identify the implications of a false negative FOBT in the population tested. Method Data from the National Bowel Cancer Audit Programme from three centres in the FOBT age group (60–74 years) over 2 years (August 2011–2013) were linked for their FOBT screening status to the Eastern FOB hub. Comparisons were done primarily between two groups: the interval cancer group (cancers diagnosed between 2 yearly FOBT screening rounds) and the non-uptake group (patients who were offered but declined FOBT screening). Demographics, presentation, tumour characteristics and survival were compared. Tumours from and distal to the splenic flexure were classed as left sided tumours. Dukes C and D tumours were classed as advanced tumours. Results 521 colorectal cancers were diagnosed in the above population. Of these 231 cancers were diagnosed in the non-uptake group and 128 were diagnosed in the interval cancer group. Both the non-uptake group and the interval cancer groups were comparable in age ranges (mean age in years (+/− 1SD); 68(4.2) and 67(3.8)); gender distribution (Males (%); 133(58) and 84(66)) and location of tumour (left sided (%); 165(71) and 79 (62))as well as for ethnicity and deprivation indices. The interval cancer group were more likely to present with an advanced tumour (Dukes C/D) compared to the non-uptake group (89(70%) vs. 125(54%);X2=8.1; p = 0.004). The median time between diagnosis and death in the interval cancer group was 10 months (0–34 months) compared to 13 months (0–34 months) in the non-uptake group. The 1 year mortality in the interval cancer group was also higher (n = 20; 16%) compared to the non-uptake group (n = 27; 12%). All except 2 patients in the interval cancer group had underlying ongoing ‘red flag’ symptoms with anaemia being present in 36 patients (28.1%; (mean) Hb 10.3 gm; MCV 82.4;MCH 26.3). Conclusion We report a poorer outcome in patients who had a false negative FOBT compared to those patients who had declined the test. Though this may in part be explained by duration bias, we highlight the possibility that the ‘false negative’ result may have had a detrimental effect of falsely reassuring the patients who undertook the test in-spite of their underlying symptoms leading on to a subsequent delay in their seeking medical advice coupled with a natural progression of the disease. We flag up the caution that should be exercised in patients who have a negative FOBT. Disclosure of interest None Declared.