Good point, if it is altruism out of self-interest it is not altruistic in the pure sense.
I think that I might go as extreme as to say it is only altruistic if it makes you feel bad or puts you in a clearly bad position.
Let's say that out of an act of altruism you help a person achieve some goal of theirs. Now you do not have a material gain from this, but doing so will make you feel good, hence you did it to make yourself feel good?