[Evaluation of RPHA fecal occult blood test in screening for colorectal cancer].

Evaluation of reverse passive hemagglutination (RPHA) fecal occult blood (FOB) test in screening for colorectal cancer was carried out in a group of subjects (3034 persons) with history of rectal polyp and ulcer. All subjects were examined by 60 cm fiberoptic colonoscopy, RPHA and benzidine (BT) FOB tests. Among this high risk population, 10 cases of colorectal cancer and 1 case of rectal carcinoid were detected by colonoscopy and pathology. Regarding the findings under fiberoptic colonoscopy as a reference standard, the sensitivity of RPHA and BT in screening for colorectal cancer was 63.6% and 72.7%; the specificity was 81.9% and 61.7%; the general indicator--Youden index was 0.46 and 0.34, respectively. In 7 cases of colorectal cancer with both FOB tests positive, 5 (71%) had lesions in early stages (Dukes A and B). The results indicate that comparing with BT, RPHA has slightly lower sensitivity but higher specificity. RPHA fecal occult blood test could be used as preliminary screening for colorectal cancer.