Odd. Lets start with the basics. First, try this:
IIf(Cdbl([3 laboratory values]![preop sodium])<135 Or Cdbl([3 laboratory values]![preop sodium])>145,[3 laboratory values]![preop sodium],"-")
If that doesn't work, would you mind answering these questions?
1) Is [3 laboratory values] a table or query?
2) What is the data type for [preop sodium]?
3) Is [3 laboratory values] included in your query as a source table?
~Abby