Understanding a White Blood Cell Shift: What Does It Mean?

Question
what does a shift (left, etc.) in white count mean?  I think you look at the segs, is that correct?

Answer
Left shift refers to a greater amount of acute inflammatory white cells, i.e. segs and bands.  "Left" refers to earlier in the time line of development of polymorphonuclear (or "polys") cells.  These are the cells that are typically involved in fighting off infections.  A left shift indicates that more of the early, less mature white blood cells are being called upon to help fight the infection.  Sort of "bringing in the reserves".