A "CS5 test" when referring to T and B cell subsets typically indicates a test that specifically looks for the presence of the CD5 marker, which is commonly used to identify a subset of B cells, particularly in conditions like chronic lymphocytic leukemia (CLL) where a high percentage of CD5 positive B cells may be present; however, it's important to note that CD5 can also be expressed on a small population of T cells as well.