Approval Procedure Query

Dear All,

I have created an approval procedure on PO based on total amount as below. 

SELECT 'TRUE' where exists (

  SELECT T0.CardCode FROM OCRD T0 

  WHERE T0.CardCode=$[$4.0.0] AND ($[opor.doctotal.number]-$[opor.vatsum.number]) between 0 and 250000)

The requirement is to check the amount based on currency, how should i proceed with it?  Please advise.

Note: LC - USD

Thanks and Regards,

Lailus