Abstract
An established chemical faecal occult blood test (Haemoccult prepared without rehydration) has been compared with a new immunological test (Hemeselect) in patients referred for investigation of lower gastro-intestinal symptoms. Hemeselect was shown to have a higher sensitivity for colorectal carcinoma (94.0% compared with 58.0%), the greatest difference in sensitivity between the two tests being for rectal cancers. Similarly Hemeselect was more sensitive than Haemoccult for colorectal adenomas (66.6% vs 33.3%), and for inflammatory bowel disease (88.9% vs 33.3%). However the enhanced sensitivity of Hemeselect for colorectal neoplasia and inflammatory bowel disease was accompanied by a significant increase in the overall rate of positive reactions (32.8% of patients had a positive Hemeselect reaction compared with 14.8% who had a positive Haemoccult test), and a reduction in specificity (84.1% for Hemeselect vs 96.0% for Haemoccult). Hemeselect is a more sensitive indicator of colorectal neoplasia in symptomatic subjects, trials of its use as a screening test for asymptomatic neoplasia appear justified.
Highlights
Faecal occult blood tests are potentially useful in the preliminary assessment of subjects with symptoms of colorectal disease (Leicester et al, 1983) and for mass population screening for asymptomatic colorectal neoplasia
The aim of this study was to compare the sensitivity for large bowel neoplasia of Haemoccult and Hemeselect in patients with symptoms suggestive of large bowel neoplasia, such information being imperative before further evaluation of Hemeselect as a screening test is considered
Seven (33.3%) patients had a positive Haemoccult test compared with 14 (66.6%) who had a positive Hemeselect test (X2 = 4.65, d.f. = 1, P = 0.03)
Summary
Faecal occult blood tests are potentially useful in the preliminary assessment of subjects with symptoms of colorectal disease (Leicester et al, 1983) and for mass population screening for asymptomatic colorectal neoplasia. The test commonly used for screening, Haemoccult (Rohm Pharma) has an estimated sensitivity in the range 50-65% for asymptomatic cancers (Kewenter et al, 1988; Kronborg et al, 1989; Hardcastle et al, 1989) and has been noted to be insensitive for rectal and caecal cancers, missing over 50% of malignancies at these sites (Kronborg et al, 1989; Hardcastle et al, 1989). One of the proposed mechanisms for this discrepancy is that Haemoccult, which is essentially a test for the Haematin moiety of Haemoglobin, relies on an optimum degree of Haemoglobin degradation which is most commonly achieved by blood loss from sigmoid cancers
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