4 days post op Brazilian Butt Lift, I noticed blood while peeing. Is this normal?

Patients undergoing lengthy procedures such as BBL will typically have a bladder catheter placed during the procedure for monitoring purposes. Occasionally, trauma from placement of the catheter can lead to transient hematuria (blood in the urine). This should clear fairly quickly. I would recommend speaking with your surgeon to verify whether you had a catheter placed. If not, or if symptoms persist a urologic work up may be necessary. 

You'll need to check with your surgeon if a bladder catheter was used. Otherwise a work up by a physician should be performed.