I think I might be able to shed some light on this, as a 'retired' human resources professional. HR professionals walk a very tough road, in that they are responsible to share anything with other management that might effect the business, but there is also the responsibility to earn the trust of the employees and keep confidences. It would be best if employees didn't share non-work-related personal information with their HR manager, but often they feel the need to share causes for absences or reasons for wanting to leave the company or move to another position or location. Often an employee will not want you to share this information (say in the case of issues with a supervisor), possibly to avoid conflict, but it might be necessary to consider acting on this information if it reveals that there is a problem in the department that needs addressing. I think that HR people need to assure their employees that their confidences will be kept if at all possible, but if they do need to be shared, every effort will be made to deal with the situation in such a way that the employee's identity will be protected. I have also gone back to employees when I felt I was no longer able to keep what they told me confidential, and either ask their permission or at least explain my reasoning for now needing to take their information further along the chain of command. I just didn't want anyone to think that I was going behind their back or against their wishes without obtaining their understanding.
This is tricky to answer in that I don't know specifically what type of information you want kept confidential, but I hope you can come to some kind of understanding.
Jayne