The relative value of fecal occult blood tests and flexible sigmoidoscopy in screening for large bowel neoplasia

Abstract

The secondary prevention of colorectal cancer is based on the early detection of noninvasive cancer and removal of adenomatous polyps. The two commonly used screening tests are flexible sigmoidoscopy and guaiac fecal occult blood testing. Both were performed simultaneously and independently on 1176 asymptomatic volunteers followed by colonoscopic examination if either occult blood or a neoplasm was detected. Neoplasia (adenomatous polyps or cancer) were found in 48 screenees. Only ten had positive stool occult blood while 45 were detected by sigmoidoscopy. Analysis of sensitivity for neoplasia was 93.8% for sigmoidoscopy but only 20.8% for the occult blood tests, while the positive predictive values for neoplasia were 100% and 23.8% respectively. The fecal occult blood test detected only 18% of screenees with adenomas and 60% with invasive cancer. Flexible sigmoidoscopy detected 95% and 80% respectively. Analysis (kappa statistic) demonstrated little agreement between the two tests (P greater than 0.05), indicating that they are diagnosing different neoplasia. Evaluation of expected gain in diagnosing neoplasia, by combining both tests, gave 18% for the fecal blood test and 94% for the endoscopic test. These results confirm the complementary value of performing both tests, but especially the high sensitivity and predictive value positive of flexible sigmoidoscopy for adenomas, including those with severe dysplasia, and the converse for the fecal occult blood test. This latter test must be recommended and used within a screening program with caution and full understanding of its limitations.

Population based randomised study of uptake and yield of screening by flexible sigmoidoscopy compared with screening by faecal occult blood testing

“…This study confirms the greater sensitivity of flexible sigmoidoscopy compared with faecal occult blood testing for distal neoplasia but refutes the hypothesis that neoplasia detection by flexible sigmoidoscopy can be considerably enhanced by the addition of faecal occult blood testing 25. The observation that the test result was negative in many subjects who were found at flexible sigmoidoscopy to have adenomas or cancer was not surprising; all of the adenomas were less than 1 cm in diameter and the malignant polyp was less than 2 cm.…”

Cost-effectiveness of population-based screening for colorectal cancer: a comparison of guaiac-based faecal occult blood testing, faecal immunochemical testing and flexible sigmoidoscopy

“…the diagnosis had not been determined prior to recruitment, and all participants underwent the index test and reference standard test), which included ‘screening populations' and, for gFOBT, which used Hemoccult (Beckman Coulter, Inc., Brea, CA, USA) or Hemoccult II (Allison et al , 1990, 1996, 2007; Castiglione et al , 1991; Foley et al , 1992; Itoh et al , 1996; Brevinge et al , 1997; Chen et al , 1997; Nakama et al , 2000, 2001; Lieberman and Weiss, 2001; Cheng et al , 2002; Niv et al , 2002; Gondal et al , 2003; Liu et al , 2003; Sung et al , 2003; Collins et al , 2005; Morikawa et al , 2005, 2007; Nakazato et al , 2006). Three studies were combined to estimate sensitivity of FSIG for intermediate/high-risk adenomas (Rozen et al , 1987, Lieberman and Weiss, 2001; Sung et al , 2003). As studies included few (if any) low-risk adenomas or cancers, sensitivity estimates for these parameters were based on expert clinical opinion, assuming the former would be lower than for intermediate/high-risk lesions and the latter higher.…”

Flexible sigmoidoscopy and the changing distribution of colorectal cancer: implications for screening

“…Another method of increasing the diagnostic yield of an FS screening programme would be the additional use of FOBT to detect proximal CRCs. However, FOBT is unlikely to provide additional benefit to a FS screening programme25 because: (1) FOBT may have a low sensitivity for asymptomatic proximal lesions,21 26 (2) it may be necessary to repeat FOBT every one to two years, requiring intensive patient follow up, and (3) compliance is likely to be low. However, a Japanese study of 11 333 colonoscopies carried out as part of a health checkup suggested that FS as a screening tool on its own would have missed 73.7% of proximal high risk tumours but would have missed only 62.0% when combined with immunological FOBT 27.…”