What does the Code say? 32 ILAC 422.130(n)(3) states “All valid individual measurement results shall be reported.” You are not required to communicate invalid results. You are required to document any observed tampering.
Ethical Duties. It is your ethical duty to report invalid test results, as difficult as that may be.
Fiduciary Duties. It is your fiduciary duty to your client to report invalid test results, they paid you and they expect you to be honest with them.
Maintaining the Peace. Be mindful to use tact when discussing why a result is invalid. Avoid accusing the party if possible.