Well first they make you do a bunch of urine tests. the funnest is when they make you collect a 24 hour urinanalysis and keep it in your fridge.
Then the nephrologist looks over the number and determines how your kidneys are functioning.
I'm going through this right now. I was just told that someone my age should have 100% kidney function. I have 60-70%
THe next step is to take an ultrasound to make sure there is no blockage or anything like that.
Then there is the kidney biopsy where they take about 4 needles and take a sample from your kidneys.
From there they determine why it's not working properly ie due to scaring, inflammation, lupus, sojugren's etc.
For me, the good news is that there is no white blood cells in my urine... meaning that it's probably not cause by lupus, but probably by sojogren's.... since lupus is much more aggressive in its attack on the kidneys.
I am lucky to have 3 of my doctors working in the same hospital together and they contact each other frequently. My rheumi even tells me that she will make sure to look over everything the nephrologist theorize so that way I will always get at least two opinions.
After the biopsy, where they will determine what is causing renal failure, then they can determine what drugs to give you.
I went through similar...I was showing protein and red blood cells in urine for 6 weeks. Dr did a 24 hour collection (all the pee in one jug for 24 hours and draw 1 vial of blood for hemocrit) and kidney sonogram.
I have very mild issue with my kidneys, but no scarring or blockage. Dr said they would continue to monitor and refer to nephrologist for a biopsy only if the condition gets worse.
I have been on immunosuppressants for a while, have been on 1000 mg of cellcept a day for 8 or 9 months. Dr said that was what saved them from worse damage...they added steroids for while and all seems to have leveled out, but I get urine and blood tests every 8 weeks.
Kidney involvement differes for everyone from mild like mine to severe, you need to work very closely with your Dr and ask questions about what you do not understand.