would you please clarify what you mean by "test cases"? Are you referring to Coded Steps?
If so, you can declare and use global variables in the "code behind" class where all the coded steps are stored.
Just make sure you declare them inside the class but outside each individual method (coded steps are represented as methods). From here all methods (i.e. coded steps) in your test can access it. See screenshot 1.
the Telerik team