I have interstitial cystitis and lupus. UA lately has been showing moderate blood in urine but no RBC. Do I just assume it's from the IC?

Assume nothing. Do not assume the cause of the bleeding present, rather see your FP or Urology MD for confirmation. The ultimate fate of your kidneys is at risk if you assume and are wrong.
Yes,most likely. advise check on urine protein , IC and SLE can go together. IC not assocoated with kidney damage but lupus ca. Strongly suggest 24 hour urine protein determination.