When the encounter is solely for the chemotherapy treatment, I understand that Z51.11 or Z51.12 should be the principle diag listed. My confusion begins when all the lab work is included on the same claim form. Does the Z code still need to be in the principle diag position instead of the neoplasm code? Will all the labs still pay with a Z code as prime diag? We are having an issue of header level diag versus line level diag. Also confused if it applies to Professional as well as Facility. I appreciate any feedback.