After insert/update trigger on specific columns and with a where clause

I need to create a trigger that will track changes to a few specific columns on the qa_results table (by inserting the old and new values into another custom table), but I only want to get the rows for a specific plan_id. I also want to capture inserts when those specific columns meet certain criteria. I've seen examples of triggers on specific columns, but can't find anything with both specific columns and restricting it to certain rows in the source table, i.e., the plan_id. Any examples would be very much appreciated!