Hi Melodie, i think testing nk cells during a flare would probably only affect its numbers not neccessarily its ability to function, if that makes sense, but dont quote me. I have written on here before about lymphocyte subset testing, i have found they seem to follow my symptoms, especially my cd8 lymphocytes. These slowly came down while i was on antivirals as well as symptom improvement, but of late, the last few months have been feeling quite buggered, a recent lymph test showed they are all elevated again. All i can put this down to maybe is changing from famvir to valtrex at the beginning of the year. Elevated lymphocytes can indicate an infection, i also recently read where if nk cell function is poor, other parts of the immune system try to take the slack eg increase in t-cells(lymphocytes), which i think is whats happening with me. I do have a few things up my sleeve Im looking into to strengthen nk cells but this is also dependent on if i can do some of these things while in this cfs study as it could upset there results.