Hi, i need to check duplicates for userid and email fir the following code....please help

global class InboundLinxUserRegistration {
      global class dtRegistrationInput {
      webservice ID UserId;
      webservice String First_Name;
      webservice String Last_Name;
      webservice String Email_Address;
      webservice String Status;
      webservice ID Workplace_Id;
      webservice String Workplace_Name;
      webservice String Workplace_Province;
      webservice String Workplace_City;
      webservice String Workplace_Postal_Code;
      webservice String Workplace_Address;
      webservice String Speciality;
      webservice String Record_Type;
        }
     global class dtRegistrationOutput {
       webservice date mydate;
       webservice string added;
       webservice String status;
       webservice String Message_Text;
      }
     
      public webservice static dtRegistrationOutput userregistration(dtRegistrationInput userregistration){
           dtRegistrationOutput retvalue=new dtRegistrationOutput();
           retvalue.status='Success';
           Account acc=new Account();
           acc.National_Code__c=userregistration.UserId;
           acc.FirstName=userregistration.First_Name;
           acc.LastName=userregistration.Last_Name;
           acc.PersonEmail=userregistration.Email_Address;
           acc.Account_Status_NES__c=userregistration.Status;
           acc.Primary_Parent_vod__c=userregistration.Workplace_Id;
           acc.Primary_Province_NES__c=userregistration.Workplace_Province;
           acc.Primary_City_NES__c=userregistration.Workplace_City;
           acc.Primary_Postal_Code_NES__c=userregistration.Workplace_Postal_Code;
           acc.Primary_Address_1_NES__c=userregistration.Workplace_Address;
           acc.Specialty_1_vod__c=userregistration.Speciality;
           acc.RecordTypeId=userregistration.Record_Type;
                     try{
                     insert acc;
                      } catch(DMLException e) {
                                retvalue.status='Failure';
                                retvalue.mydate=system.today();
                                retvalue.added='false';
                                retvalue.Message_Text=e.getMessage();
                      }catch (Exception e){
                            retvalue.mydate=system.today();
                            HttpRequest req=new HttpRequest();
                            Http http=new Http();
                            HttpResponse res = http.send(req);
                            System.debug('STATUS:'+res.getStatus());
                            System.debug('STATUS_CODE:'+res.getStatusCode());
                            retvalue.Status='Failure';
                            retvalue.Message_text=e.getMessage();
                         }
                                          
                    return retvalue;
       }
  }