survey web app: tracking the end user

survey web app: tracking the end user

I am looking for some guidance please.
Problem: A patient goes into hospital for an operation. They are seen a
number of years later for a follow up appointment. This appointment takes
place in a hospital clinic setting which requires valuable hospital
resources.
Solution: Instead of returning to the hospital for their follow up
appointment, they go online and complete a web app survey.
Problem of solution: Cannot allow personal data to cross the www.
Solution to problem of original solution: Send email to patient with
hyperlink to the web app survey with a unique identifier(UI) contained in
a query string. This arbitrary UI would have previously been assigned to
the patient at an earlier date. When the patients uses the hyperlink
contained in their email, the UI can be extracted from the query string to
reconcile their survey answers to their medical record.
I'm not hell bent on following this exact methodology. It is my idea, it
could very possibly be rubbish.
Please let me know if this is a good way to go or if not maybe an
alternative?
Thank you very much for you time. Much appreciated.
kind regards Paul .