I am interested in benchmarking how other pharmaceutical companies determine whether/when to investigate Extraneous/UnexpectedImpurity Peaks.

-What impurity analyses require an investigation for extraneous peaks?
All impurity analyses?
API Related Substances only?
Residual Solvents as well?
Other?

For those impurity analyses that are not in scope, what is the rationale for excluding them?

-What thresholds do you apply below which an investigation of extraneous peaks is not required?
For example, do you investigate newly appearing unspecified impurities that are below the unspecified impurity specification but above the method's Limit of Quantitation?

Or is an investigation only initiated when a peak approaches or exceeds the unspecified impurity specification?

-Finally, are you aware of any guidances that address this subject?

I greatly appreciate your feedback.