c# fix ค่า ใน prameter sql ออก พอรับค่าจากฟอร์ม ไม่ออก

public string getPk_id, getHcode, getAcode;  // รับค่าจาก form ก่อนหน้า

        private void Form2_Load(object sender, EventArgs e)
        {      
            
            DBConnect Conn = new DBConnect();

            string sql = "SELECT pt.pk_id,pt.id,pt.hn,pt.death_status,pt.ttl,pt.name,pt.lname,pt.born, ";
            sql += "pcu.name_sub,pt.hcode ";
            sql += "from patient pt ";
            sql += "left outer join ref_pcu_child pcu on pt.hcode = pcu.hcode ";
            sql += "where pt.id = '" + getPk_id + "' and pt.acode = '" + getHcode + "' and pt.hcode = '" + getAcode + "'";
           //sql += "where pt.id = 'xxxxxx' and pt.acode = 'xxxxx' and pt.hcode = 'xxx' ";

       
            DataSet ds = new DataSet();
            ds = Conn.returnDataSet(sql);

            cmbPreName.Text = ds.Tables[0].Rows[0]["ttl"].ToString();
            txtFname.Text = ds.Tables[0].Rows[0]["name"].ToString();
            txtLname.Text = ds.Tables[0].Rows[0]["lname"].ToString();

            label2.Text = ds.Tables[0].Rows[0]["death_status"].ToString();
           
        }