Fecal Occult Blood Test (FOBT)
In FOBT testing, a person collects stool samples that are analyzed for the presence of small amounts of blood. Collection details vary somewhat for different tests, but typically involve collection of as many as three different specimens on 3 different days, with small amounts from one specimen smeared by a wooden stick on a card with two windows or otherwise placed in a specimen container.
The guaiac test identifies peroxidase-like activity that is characteristic of human and nonhuman hemoglobin. Thus, it will record blood from ingested meat, upper airway bleeding such as epistaxis, upper gastrointestinal (GI) bleeding, as well as colonic lesions.
Five controlled clinical trials have been completed or are in progress to evaluate the efficacy of screening utilizing the FOBT. The Swedish trial is a targeted study for individuals aged 60 to 64 years. The English trial selects candidates from lists of family practitioners. The Danish trial offers screening to a population aged 45 to 75 years who were randomly assigned to a control or study group.[3,4]
The Minnesota trial demonstrated that annual guaiac-based FOBT (gFOBT) testing using primarily rehydrated samples decreased mortality from colorectal cancer (CRC) by 33%  and that biennial testing developed a 21% relative mortality reduction. Some part of the reduction may have been attributed to chance detection of cancer by colonoscopies; rehydration of guaiac test slides greatly increased positivity and consequently increased the number of colonoscopies performed. Subsequent analyses by the Minnesota investigators using mathematical modeling suggested that for 75% to 84% of the patients mortality reduction was achieved because of sensitive detection of CRCs by the test; chance detection played a modest role (16%–25% of the reduction). Nearly 85% of patients with a positive test underwent diagnostic procedures that included colonoscopy or double-contrast barium enema plus flexible sigmoidoscopy (FS). After 18 years of follow-up, the incidence of CRC was reduced by 20% in the annually screened arm and 17% in the biennially screened arm.
The English trial allocated approximately 76,000 individuals to each arm. Those in the screened arm were offered nonrehydrated gFOBT testing every 2 years for three to six rounds from 1985 to 1995. At a median follow-up time of 7.8 years, 60% completed at least one test, and 38% completed all tests. Cumulative incidence of CRC was similar in both arms, and the trial reported a relative risk (RR) reduction of 15% in CRC mortality (odds ratio [OR], 0.85; 95% confidence interval [CI], 0.74–0.98). The serious complication rate of colonoscopy was 0.5%. There were five deaths within 30 days of surgery for screen-detected CRC or adenoma in a total of 75,253 individuals screened. After a median follow-up of 11.8 years, no difference in CRC incidence between the intervention and control groups was observed. The disease-specific mortality rate ratio associated with screening was 0.87 (0.78–0.97; P = .01). The rate ratio for death from all causes was 1.00 (0.98–1.02; P = .79). When the median follow-up was extended to 19.5 years, there was a 9% reduction in CRC mortality (RR, 0.91; 95% CI, 0.84–0.98) but no reduction in CRC incidence (RR, 0.97; 95% CI, 0.91–1.03), or death from all causes (RR, 1.00; 95% CI, 0.99–1.02).