Passing a key, inserting into database

I have a patient form that has a link on it. When the link is clicked, I pass the patientkey to a dialog. The dialog has a button named "Activate Patient." When the button is clicked the patientkey & entry date are being inserted into the patient access table. In my SQL statement I am checking for duplicates, using the patient key.
 
Select @dupCount = Count(PatientKey)
From PatientAccess
Where PatientKey = @PatientKey
If @dupCount > 1 GoTo DUPLICATE_ERROR
 
When I click the "Activate Patient" the first time, it activates the patient.
When I click the "Activate Patient" the second time it creates a duplicate patientkey into the table. When I click it a third time it finally throws up a duplicate error. I don't know if using the patient key to check it is the best option or not.
 
Question: In the dialog, after the passing the patientKey, is there a way for me to obtain the PatientAccessKey so I can use that to check duplicates against? What would be the best way? All help is welcomed! Thanks!
 
PatientAccess Table
PatientAccessKey (PK) Identity field
PatientKey
EntryDate