Hi anniewi, and thanks for your post and question. It is a good one! You may be aware we cannot provide medical advice or diagnostics over the internet (for your own safety), but your concern certainly warrants a reply.
In the most general of terms, the CO2 level provided for a metabolic test may be somewhat related to the arterial CO2 but, it is not a true indication of what is happening acutely. It really is only the arterial blood gas sample (of CO2) that actually telegraphs CO2 retention.
For the best answer to your question and, most importantly, how it relates to your specific condition, you may want to discuss this with your physician. The doctor will be able to explain to you the results of the metabolic blood work, and how it reflects your particular condition.
What do you think?
Leon (site moderator COPD.net)