I've tried researching an answer to your question but not got very far. However I did come across a few links (and possible sources of information which might help), so I thought that I'd post anyway. (I apologise if this response simply wastes your time).
The basic definition of C02 is the easy bit. (It's after that when things get harder!). The human body absorbs oxygen through the lungs. It's then transported to the body's organs via the bloodstream (i.e. in your arteries). The organs use the oxygen and produce waste products. These include carbon dioxide (CO2), which is transported back to the lungs through the bloodstream (in your veins) and then exhaled. So the blood in your veins always carries CO2. I'm guessing that your test results have shown these levels to be rather high but I've no idea what that signifies.
However, the British Liver Trust has a free helpline, which is available from 0900-1700 Mon-Fri. They may well be able to answer your question:
0800 652 7330.
You might also find further information on their website:
http://www.britishlivertrust.org.uk/home/the-l iver/liver-diseases/primary-biliary-cirrhosis. aspx
The PBC Foundation might also be able to provide information and support:
http://www.pbcfoundation.org.uk/Home.htm
Lastly, the NHS website might provide you with some information:
http://www.nhs.uk/Conditions/Primary-biliary-c irrhosis/Pages/Introduction.aspx?url=Pages/wha t-is-it.aspx
Again, I offer my apologies if I've wasted your time but I ho