Will A Cystatin C Test To Be Done For Autoimmune Hepatitis?

Hi, my name is Audrey. Dx with autoimmune hepatitis, now in biochemical remission. Extensive cirrhosis. Also recently dx stage 3 chronic renal disease. Been to 2 nephrologists and they have done 1 ultrasound, rt side only. a year and half ago indicated possible medullary sponge kidney. My HGB is 10-11.4; RBC= 3.4; creatinine= 1.5-1.8; eGFR 28-35. Taking 50 mg Azathioprine and 5mg cortisone daily. I ve heard that with cirrhosis and CKD Cystatin C is a more accurate and important way to assure correct GFR. I don t get any answers to my questions. REsponse is just, there s nothing we can do. But other than lab tests and US, nothing has been done and I seem to be getting worse. My primary care phys ordered a US of my left kidney to at least see if there is a problem. Do you think I would be right in asking for the Cystatin C test be done to obtain an accurate picture of the situation? Thank you so very much. I am 68 yr old female and always very active, never smoked or drank.