PostbackURL in linkbutton

I have a linkbutton with an onClick event;

<asp:LinkButton ID="lbFileUpload"    OnClick="FileUpload_Click" Text="File Upload" runat="server"  ></asp:LinkButton>

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In the onClick event, I have a postbackURL. I put a debug step and it goes thru the step below but it stays on the same page:

 

protected void FileUpload_Click(object sender, EventArgs e)
    {
        lbFileUpload.PostBackUrl = "~/Main/FileUpload/DefaultFile.aspx?pageTitleId=39&patientId=" + PatientId;
    }

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Now, If i have the PostbackURL in the aspx page, it works. I dont want it in the aspx page because I dont know how to add that "patientId"  <%# Eval("PatientPhone")%>  to the end of postbackURL.

Howcome it stays on the same page even tho it goes thru the onClick event?