Fecal occult blood testing

In a Minnesota study of 46,501 participants age 50-80 years with annual FOBT analysis with rehydrated samples a decrease of 13 year cumulative mortality from colorectal cancer by 33% was noted (and in a biennial screening group, by 21%).

Main limitation is limited specificity.

Two types of fecal occult blood tests are currently available: guaiac-based and

Recently a fecal test to assess for alterations in exfoliated DNA has become available.

FOBT testing has low sensitivity ranging from 1% to 27% and 50% for colorectal cancers.

USPSTF defines hi-sensitivity fecal occult blood testing as having sensitivity for cancer are greater than 70% in the specificity of greater than 90%.

The guaiac fecal occult blood test is based on the detection of pseudoperioxidase activity of heme in human blood.

The fecal immunochemical test (FIT) directly detects human globin within hemoglobin in stool.

Unlike the guaiac FOBT, FIT does not require dietary restrictions and a single testing sample is sufficient.

FIT is more sensitive than guaiac FOBT demonstrating a higher sensitivity for cancer compared with high sensitivity guaiac FOBT, 82% versus 64%.

Specificity for FOBT is approximately 98% makes it a better confirmatory test than a screening test due to the positive predictive value ranging from 5 to 10%.

Using three separate stool samples collected at home is an effective strategy for reducing colorectal cancer incidence and mortality, and conversely a single sample acquired during a digital rectal examination will miss 95% of cases of advanced colorectal cancers.

Immunological fecal occult blood tests (iFOBTs), in contrast to FOBTs, which is guaiac based, to react to globin, which is degraded by proteases during its passage through the gastrointestinal tract.

Fecal immunochemical testing is superior in terms of screening participation rates and detection of colorectal cancer.

The use of low-dose aspirin may increase sensitivity of iFOBTs by increasing the likelihood of bleeding from colorectal neoplasms and is associated with the higher sensitivity for detecting such lesions, compared to a no aspirin group, with only slightly lower specificity ( Brenner H et al).

In a controlled trial involving asymptomatic adults age 50-69 years, comparing one time colonoscopy in 26,703 subjects with fecal immunochemical testing (FIT) every two years in 26,599 subjects with a primary outcome of death from colorectal cancer at 10 years: subjects in the FIT group were more likely to participate in screening than the colonoscopy group and the numbers of subjects in whom colorectal cancer was detected was similar in the two groups, but more adenomas were identified in the colonoscopy group (Quintero E, et al).

Every positive FOB test requires follow up with a more expensive and more invasive test, which may lead to unnecessary procedures based on false positive results.

Investigators linked FOBT results for 133,921 screened individuals who ranged in age from 50 to 74 years to mortality data from the National Records of Scotland Database: individuals with positive results had a considerably higher risk of death not only from colorectal cancer but also for noncolorectal cancer causes combined after adjustment for age, sex, deprivation, and prescribed medicines.

In the above study the higher risk of death held for mortality related to circulatory, respiratory, digestive, endocrine, neuropsychological, and other causes.

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