Combining Value Sets
Combining Value Sets work similarly to the Combining reference sets feature. Combining Value Sets enables users to create a new Value Set by merging two existing ones. Combining Value Sets can be performed either by invoking the Tools > Combine Value Sets… menu or by right-clicking on a Value Set and selecting 
Combine…
The following methods are available to combine two Value Sets named A and B:
Method
Math Formula
Description
Union
A U B
The resultant set contains all the elements in either A or B or both
Intersection
A Ո B
The resultant set contains the elements present in both A and B
Complement
A-B - A\B
The resultant set contains everything in A but not present in B
Complement
B-A - B\A
The resultant set contains everything in B but not present in A
Symmetric difference
(A\B) U (B\A)
The resultant set is the intersection subtracted from the union
After selecting one of them, click the Next button. To complete the operation, the Preferred Term and source for the new combined Value Set needs to be set on the last wizard page.
Hit the Finish button and the new Value Set is created. Its editor opens automatically.