fluid collection 

fluids in the body often pool around the newly transplanted kidney, because small vessels were disrupted during surgery; over several weeks, these vessels will seal themselves off and the fluid is not a big problem; however, if there is a great deal of fluid, it can cause swelling of the leg closest to the new kidney, or it can even block off the flow of urine from the kidney to the bladder, and the fluid must be drained surgically.