My baby have hb e beta thalassemia.one doctor advised to get transfusion when hb will be 8 and another advised when it will be 7.5. pls advised.

Life is not exact: Real life is never exact. So, 7.5 and 8.0 are pretty much the same number. A parent can ask her baby's own pediatric hematologist what is the preferred number, and as why. If her baby has 2 such doctor's saying slightly different numbers, the parent can go with the doctor she thinks she will be staying with the longest (as that doctor will be providing more of the care over the years).