My Mom had a stroke a few years ago (years of smoking, being overweight, no exercise, etc.) and is now in a nursing home. Recently, her nurse gave me a copy of my Mom's meds and I noticed some had a DX: footnote, like DX: COPD under her inhaler. My understanding of DX Codes is that they are diagnostic codes, i.e., my Mom has been diagnosed with COPD. Is this a correct assumption?

If your mother is using an inhaler then the reaon for this is a diagnosis of Chronic Pulmonary Obstructive disease. Dx means diagnosis. COPD is a bit of a catch all diagnosis for a lot of conditions however.