How can lupus impact complete blood counts? Just going for initial tests

Hi,

I visited my doctor today as I have low neutrophils and low white blood count and this has been going on for long enough that it's 'chronic.' (Neutrophils: 1.21 in September 2023, now 0.9. WBC: 2.6 in September, now 3.5) I was going over some other things that have popped up recently like joint pain and my doctor cut me off pretty much straight away and has said she is sending me for tests for lupus, rheumatoid arthritis and inflammatory conditions. I then looked up the symptoms of lupus and admittedly whilst I identify with some symptoms (ulcers, photosensitivity, rashes, and previous bouts of chest pain), I was surprised my doctor wanted to send me for these tests with me only mentioning joint pain.

I suppose my question is, how are these blood results indicative of inflammatory conditions? If so, what is the connection? I am not asking for medical advice, more interested in how the connection works between my labs and my doctor wanting to test me for an inflammatory condition before I had barely sat down!

Thank you. Since I gave left the doctors 2 hours ago, I have had left wrist pain and twinges, right wrist pain and twinges, knee joint pain and a rash on my hands that popped up as soon as I went outside, so I am hoping to have some answers soon!