The factor responsible for the left shift of Hb-O2 dissociation curve is
Hb-O2 dissociation curve shift to left indicates more affinity of Hb to O2 and thus less delivery of O2 to tissues.
Shift to left seen in
-        Increased pH
-        Decreased 2,3 DPG, temperature, PCO2
-        HbF (Fetal)
Shift to right seen in
-        Decreased pH
-        Increased 2,3DPG, temperature, PCO2
-        HbS (Sickle cell)
Increase in 2, 3 DPG in RBC
Fall in temperature
Fall in pH
Increase level of CO2 blood