The "Seattle Protocol", introduced about 20 years ago, calls for biopsies to be taken quadrantically over each centimetre length of the suspected area.
It's sometimes not that easy to tell exactly where the suspected Barrett's begins and ends - and it's unlikely to be a tidy ring as in this picture - far more likely to have tongues or islets and the surface of the oesophagus isn't nice and smooth.
The Seattle protocol has come in for discussion with research papers appearing to contradict each other [t-i][t-ii].
A good endoscopist may be able to spot the suspect areas but it can be like looking for a needle in a haystack.
How quickly can you spot the odd one out below?
Attempting to make the identification of suspect cells easier, various techniques have been used including spraying the oesophagus with vinegar which makes areas of Barrett's show up better.
And new endoscopes are now available with in-built microscope functions.
The mined biopsies, each the size of a grain of rice, are placed in a fixative to preserve them and sent to the pathology laboratories where they are embedded in paraffin wax. When set, this is then sliced very thinly to create microscope slides to be examined by a skilled histopathologist looking at the structure of the cells. The presence of columnar, "goblet" cells is indicative of Barrett's Oesophagus.
The image on the right shows a typical microscope slide (annotated) where Barrett's cells have been discovered.
The pathologist must also determine whether the cells have started on a course which could lead to cancer, "dysplasia". (See the page on Barrett's Oesophagus.)