Dynamic LoadVars

Hello everyone. Thanks in advance for any help. I am working on a project where I need to check if my loaded variables contains a certain variable name. Basically i want to do the following:
I have an string that contains a name;
I want to pass the value of the string to my loadvars variable.
If a variable with this name exists, I want the data to be displayed in a text box

Here is some code that I am using:

_global.getcaptions = new LoadVars();

stuff=“test”;

_root.caption.text=_global.getcaptions.stuff;

I think the trouble is that the call to getcaptions is treating stuff as a variable name instead something which holds another variable. How do I pass dynamic variable names to a LoadVars variable?

Thanks again for any help