Hemiglobin lost post op. 2 days after total knee replacement my wife hemiglobin level dropped 1 point in 6 hrs from 8.7 to 7.7 is this normal?

Blood loss. Check with orthopedic surgeon who did the surgery. It may be acute blood loss, hemo dilution from IV fluids, or testing variability.
Blood lose. Not uncommon post operatively can imply hemorage but could also be dilutional blood count dropping from intravenous fluids.