Wednesday, 16 August 2017

FAECAL OCCULT BLOOD TESTING

Guaiac-based faecal occult blood tests 
 Guaiac-based faecal occult blood tests have proven characteristics that make them suitable for population screening. They lack the analytical specificity and sensitivity of immunochemical tests, their analysis cannot be automated and the concentration at which they turn from negative to positive cannot be adjusted by the user. For these reasons guaiac-based tests are not the preferred test for a modern population screening programme, although depending on local labour costs, the mechanism of kit distribution and collection and reduced sample stability in immunochemical testing, they might prove more practicable and affordable than immunochemical testing 

Immunochemical faecal occult blood tests

Immunochemical tests have improved test characteristics compared to conventional guaiac-based tests. They are analytically and clinically more sensitive and specific, their measurement can be automated and the user can adjust the concentration at which a positive result is reported. Immunochemical tests are currently the test of choice for population screening; however, individual device characteristics including, ease of use by the participant and laboratory, suitability for transport, sampling reproducibility and sample stability are all important when selecting the iFOBT most appropriate for an individual screening programme

DNA and other related new markers  

Only tests for blood in faeces have been demonstrated to have the necessary characteristics to be suitable for population screening. DNA and other related new markers are currently unsuitable for screening, either singly or as members of a panel of tests

Sample stability between collection and analysis  
Whilst a maximum period of 14 days between collection and analysis is quoted for many guaiac faecal occult blood tests, that quoted for immunochemical tests is significantly shorter. Until more stability data are published, screening programmes should adopt the conditions and period of storage described in manufacturer’s Instructions for Use having determined that they are appropriate for local conditions which might expose samples to high temperatures for long periods of time


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