Population screening for colorectal cancer: comparison between guaiac and immunological faecal occult blood tests.

There is concern about the low sensitivity of the guaiac-based Haemoccult test in mass population faecal occult blood (FOB) screening for the early detection of colorectal carcinoma. Hemeselect, an immunological FOB test, has been shown to be more sensitive for symptomatic colorectal cancer and may prove to be a more reliable screening method. In Brighton and Guildford, 4018 asymptomatic subjects aged 50-75 years were offered screening with Haemoccult and Hemeselect. A total of 1489 (37.7 per cent) completed both tests, of which 17 (1.1 per cent) were positive for Haemoccult and 145 (9.7 per cent) positive for Hemeselect (a total of 148 subjects had positive tests). Seven subjects (4.7 per cent) refused to be investigated. Colonic investigation in the remainder revealed nine cancers and 49 patients with 67 adenomas (32 tumours 1 cm or more in size). All cancers (Dukes A, six; B, one; C, two) were detected by Hemeselect (positive predictive value 6.2 per cent) but only one patient was Haemoccult positive (positive predictive value 5.9 per cent). Hemeselect detected 65 adenomas (31 of 1 cm or more) in 48 patients (positive predictive value 33.1 per cent) compared with 11 adenomas (seven of 1 cm or more) in eight patients who were positive for Haemoccult (positive predictive value 47.1 per cent). The test specificity for neoplasia was respectively 94.9 and 99.6 per cent. The Hemeselect positive rate is high but its substantial positive predictive value for cancer warrants continuing evaluation.