JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
A technician at a NHS Bowel Cancer Screening Centre in Surrey, UK, checks a test kit for faecal occult (hidden) blood, which would indicate the possible presence of polyps or cancer within the bowel. The kit relies on the reaction of blood with guaiac in the presence of hydrogen peroxide, when blood traces turn blue. The development of blue positive results triggers an invitation for participants to attend a clinic to discuss the need for further tests.
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