Question : Cannot get DateDiff query to work

I have a table (tblSynched) with 5 colums. Each colum in this table has the name of another table in the database. Everytime a table in the DB is updated the current datetime is updated in tblSynched.

A stored procedure can be called to get the latest date in tblSynched (LUD :Latest Update Date). My problem is that I also want the SP to return the number of days between the current date and LUD.

My attached code gives me the error "Procedure usp_LUD, Line 20 Invalid column name 'LUD'.

I am at a lose. please someone, anyone help! Sample tables below (given that the current date is 2010-08-23 11:18:00

tblSynched:
tbl1 tbl2 tbl3
2010-08-18 10:18:00 2010-08-19 01:18:00 2010-08-21 11:18:00

SP:
LUD DAYS
2010-08-23 11:18:00 2

         
          SELECT 
	(CASE WHEN tblItem > tblBOM AND tblItem >tblFSB_TA AND tblItem > tblRev AND tblItem >tblMisc THEN tblItem
		  WHEN tblBOM > tblFSB_TA AND tblBOM > tblRev AND tblBOM > tblMisc THEN tblBOM
		  WHEN tblFSB_TA > tblRev AND tblFSB_TA > tblMisc THEN tblFSB_TA
		  WHEN tblRev > tblMisc THEN tblRev END) AS LUD, DATEDIFF(DAY,GETDATE(),LUD) AS DAYS
	FROM tblSynched

Answer : Cannot get DateDiff query to work

SELECT
      CASE WHEN tblItem > tblBOM AND tblItem >tblFSB_TA AND tblItem > tblRev AND tblItem >tblMisc THEN tblItem
            WHEN tblBOM > tblFSB_TA AND tblBOM > tblRev AND tblBOM > tblMisc THEN tblBOM
            WHEN tblFSB_TA > tblRev AND tblFSB_TA > tblMisc THEN tblFSB_TA
            WHEN tblRev > tblMisc THEN tblRev END AS LUD,
      DATEDIFF(DAY,GETDATE(),
           CASE WHEN tblItem > tblBOM AND tblItem >tblFSB_TA AND tblItem > tblRev AND tblItem >tblMisc THEN tblItem
                 WHEN tblBOM > tblFSB_TA AND tblBOM > tblRev AND tblBOM > tblMisc THEN tblBOM
                 WHEN tblFSB_TA > tblRev AND tblFSB_TA > tblMisc THEN tblFSB_TA
                 WHEN tblRev > tblMisc THEN tblRev END) AS DAYS
     FROM tblSynched