Is an immunological faecal occult blood test better than Haemoccult? A cost-benefit study.

Immunological faecal occult blood (FOB) tests have theoretical advantages over their guaiac counterparts in that they are specific for human haemoglobin. HemeSelect is a semi-quantitative immunological FOB text. Faecal material is eluted into test diluent and serial dilutions are performed. The manufacturers recommend that erythrocyte agglutination at 1:8 dilution is considered a positive reaction. However, further serial dilutions can be carried out and the highest dilution at which the test remains positive determined. At 1:8 dilution, the test has been shown to be more sensitive for symptomatic colorectal cancer than Haemoccult. The aim of this study is to compare the positive rates, neoplastic yield and costs of Haemoccult with HemeSelect at various dilutions in asymptomatic average risk subjects aged 50-74. 1489 subjects satisfactorily completed both tests, 145 (9.7%) returned positive Hemeselect tests (read at 1:8 dilution, 38 patients with neoplasms > or = 1 cm) and 17 positive Haemoccult tests (1.1%). All positive Hemeselect tests were further serially diluted. As the Hemeselect dilution increased to 1:16, 1:32, 1:64 and 1:128 so the positive rate and yields of neoplasms > or = 1 cm progressively fell to 6.8% & 35, 3.6% & 20, 2.7% & 18 and 1.5% & 12, compared with 1.1% and eight neoplasms > or = 1 cm for Haemoccult. In spite of the unit cost of the Hemeselect test being greater than Haemoccult, the cost per neoplasm > or = 1 cm was lower for Hemeselect at 1:8 and 1:16 dilutions than Haemoccult. However, for an equivalent neoplastic yield, Haemoccult was cheaper. Hemeselect is a versatile test whose positive rate can be tailored according to the risk of the group being screened.