So you suspect access recirculation as a cause of drop in Kt/Vurea.
Recirculation parameters are checked by urea based two needle slow flow method and this patient is found to have a measured access recirculation of 18% which is high (normal range is up to 10%).
For more details on access recirculation, you can refer you to a hemodialysis kinetic module found here:
https://hemodialysiskinetics.coursepress.yale.edu/case-6-access-recirculation/