Detection of occult blood in stools: comparison of three gaiac tests and a latex agglutination test

The detection of occult blood in the stools is the only simple screening method for colorectal cancer. The aim of this study was to compare the results obtained with the new Hemolex kit (Orion diagnostica, Fumouze France) with those given by three gaiac tests--Hemoccult (Smithkline diagnostics), Hemofec (Boehringer Mannheim) and Hemopreuve (Fumouze) of 165 stools from patients without special diet. Seventy-one patients with at least two positive gaiac tests or a positive Hemolex test underwent colonoscopy followed, if negative, by fibroscopy: 28 had lesions of the lower digestive tract and five of the upper digestive tract. Sensitivity, specificity and negative and positive predictive value were of 70, 98, 91 and 92% respectively for Hemolex; 82, 74, 94 and 44% for Hemoccult; 94, 67, 98 and 42% for Hemopreuve and 91, 73, 97 and 46% for Hemofec. The results obtained in this study confirm the value of the Hemolex test for the detection of human occult blood in the stools whereas the gaiac tests used are influenced by dietary components (unless restricted), explaining their poor positive predictive value. In conclusion, due to their good negative predictive values, the authors recommend that screening for colorectal tumours should be based on the use of two or three gaiac tests which should be confirmed, when positive, by an immunological test for human hemoglobin.