dir id from selected value from autocomplete textbox windows appllication

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C#

iam working on windows application form
i fill textbox inside dtatagrid with autocompletet list from the code down

public void AutoComplete()
{
    AutoCompleteStringCollection AutoItem = new AutoCompleteStringCollection();
    foreach (DataRow rw in Dt.rows)
    {
    AutoItem.Add(Rw["columnname"].ToString());
    }
    texbox.AutoCompleteMode = AutoCompleteMode.Suggest;
    texbox.AutoCompleteSource = AutoCompleteSource.CustomSource;
    texbox.AutoCompleteCustomSource = AutoItem;
}

it's working good but my problem when i use one item i need to get the id for that items
to be more clear i dir items for sql db so i dir itemname & when i choose item i need to get the selected itemid
like how we do with ajax autocomplete extnder in asp.net