check if look up edit is selected

check if look up edit is selected

Here is code that i used to populate a look up edit:
Letsap.DAL.PersonDataSet dsPerson = new Letsap.DAL.PersonDataSet();
lookUpEdit3.Properties.DataSource = dsPerson.GetPersonsID();
lookUpEdit3.Properties.ValueMember = "Person_ID";
lookUpEdit3.Properties.DisplayMember = "Person_Name";
lookUpEdit3.EditValue = 0;
But I would like to check if the user selected a value, if they did, it
must move on to the next screen.
How do I do the check?