HEMOCCULT TEST PROPERTIES ACCORDING TO TYPE AND NUMBER OF POSITIVE SLIDES IN MASS-SCREENING FOR COLORECTAL-CANCER

Despite encouraging results from recent studies, there is still no con sensus to undertake mass screening using the Haemoccult test in the ge neral population. The success of mass screening for colorectal cancer depends among other things on Haemoccult test properties. In on-going screening programmes, the Haemoccult test consists of six slides and a test is considered positive if at least one slide is coloured. The ai m of this work was to study the influence of the type and number of po sitive slides on the Haemoccult test's positive predictive value and c haracteristics of screened lesions. This work focuses on 63 958 first tests in a mass screening programme in Calvados (France) among people aged 45-74 years. There was a linear relation between the positive pre dictive value for cancer or an adenoma larger than 1 cm and the number of positive slides (P<10(-4)). The positive predictive value for canc er or large adenoma was significantly higher when 4-6 slides were posi tive (44.3%) than when only 1-3 were positive (19.1%) (P<10(-4)). In t his latter group, the subjects in whom tumours were detected were youn ger and had significantly less extensive cancers. Borderline tests (no slides positive and at least one slide with a blue coloration confine d to the edges) had a positive predictive value for cancer or an adeno ma larger than 1 cm no different to that of tests with 1-3 positive sl ides. Subjects with borderline results were markedly younger than the others and had less extensive cancers and rectal localisation more oft en than the others. Our results suggest that (1) increasing the number of positive slides required to declare a test positive leads to an in crease in the positive predictive value but is not to be recommended b ecause of the sensitivity of the test and (2) considering borderline H aemoccult tests as positive in on-going and future mass screening camp aigns would allow an increase in the sensitivity of the test, especial ly for rectal cancer and low extensive tumours without any decrease in its positive predictive value.