Has anyone here ever had a DCLO test?

Hi folks, it's me, you may not recognize me because I changed my username to just my initials.

I wanted to ask if anyone has ever had a DCLO and what it showed? Mine showed that my diffusion capacity is below the lower limits of normal. This concerns me. I was told by a nurse practitioner that this was normal for an asthmatic. I'm curious if anyone else has had this test done. All my other tests are usually normal, yet my symptoms are severe. I am diagnosed with moderate persistent asthma. They upped my maintenance med per my request.