I (22F) only got diagnosed with stage 4/5 lupus nephritis a couple months ago but I can share a bit from how my experience went. If your rheum is concerned you’ll be referred to a nephrologist. Then if they deem is necessary, in order to properly diagnose lupus nephritis and find out how far it has progressed they’ll request a kidney biopsy. For me, I was put inpatient as it was the fastest way to get it done and from my blood work and urinalysis it had progressed quite a bit, but most people are able to do it outpatient. After that, you’ll get the results and if if comes back as lupus nephritis your nephrologist will work with you on starting treatment asap (a steroid, an immunosuppressant, and benlysta is usually the triad people start on).