International classification of function proposes the following categories for body functions: mental, sensory and pain, voice and speech, cardiac, respiratory and immune functions, genitourinary and reproductive functions, movement-related, and skin functions. Report the results both in absolute terms and relative to the comparator.
Trials and observational studies with functioning as an outcome. The instruments for outcome reporting should be validated
ICF http://apps.who.int/classifications/icfbrowser