How do I detect a change to a blob datawindow column using the db ole in powerbuilder 10

I am trying to give the user a way to save multiple form types from a single source i.e. word doc, excel, powerpoint. I can open up the various applications and save and retrieve the information. My problem is how do I detect a change to the document so I don't have to prompt the user to save when nothing has changed. I used get changes, compared get full state blob legnths but none of this is effective.
Thanks
LW