Hi Manal,
No, it doesn't guarantee an increase in hgb. For many Thals, it helps in the beginning, but things eventually go back to the way they were. Doctor's these days don't like to shoot straight for the spleen, and usually only remove it when it's extremely large and/or malfunctioning. It depends on what country you live in, also. Doctors do different things in different places. Here, in New York, doctors don't like removing the spleen unless absolutely necessary.
I have, though, been told by a number of Thals that removing their spleen did help with decreasing the amount of blood they needed and how often they received it. So, it really depends on the person.
As far as I know, more people with Intermedia do better keeping their hgb up after having their spleen removed than Majors do.