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faecal occult blood tests (diagnosis of colorectal cancer)

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A study published by Kronborg et al (Lancet, 1996) revealed that biennial screening with faecal occult blood testing reduced mortality from colorectal cancer.

The study involved 30, 967 adults who were assigned to biennial screening using a guaiac-based FOBT (in this case Haemoccult-II). Patients using the test were advised to have dietary restrictions before the test (no red meat, fresh fruit, iron preparations, vitamin C, or aspirin or other non-steroidal rheumatic drugs for 3 days before testing).

Two other trials (2,3) have also provided evidence that faecal occult blood testing every two years has the potential to reduce mortality by up to 20%.

A further trial by Mendel et al (4) has shown that both annual and biennial faecal occult blood screening reduced the incidence of colorectal cancer. This trial also showed, for the first time, that faecal occult blood screening can decrease both the rate of cancer and the mortality rate.

Notes:

  • two types of faecal occult blood test are now available: the Guaiaco and the Immunochemical test
    • sensitivity and specificity of the two tests are similar and do not clearly indicate which one is better for screening
    • Guaiaco test recommends three different evacuations, and requires the patient to store the samples, and follow dietary restrictions
    • immunochemical test is recommended on a single evacuation and does not require dietary restrictions
    • the associated discomfort and embarrassment of faecal sampling and the dietary restrictions have been hypothesized to be determinants of noncompliance (5)
  • the dimeric isoenzyme of pyruvate kinase, M2-PK, expressed by tumor cells, has as well been proposed as a screening tool for colorectal cancer
    • however the office-based immunochemical faecal occult blood test was found to have significantly higher specificity, positive predictive value, and positive likelihood ratio as compared with M2-PK (6)

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