Thanks for the reply Ivy, I'm a New Zealander.
The 6-TGN test stands for 6-thioguanine nucleotides. Here is a link to a NZ article on the topic
I think it is mainly used when people start on azathioprine or 6MP to adjust doses, but I have had blood tests for this for a few years now and I can't work out why the results vary.
26F, Crohn's for 8 years, currently on 6MP and pentasa. Have previously tried remicade and iron.