As Tom mentioned, it is important to consider that "How are you (doing)?" often just means that the speaker is acknowledging your presence. That means it is phatic communication, or communication only for social purposes. This can be a confusing cultural reality for someone who speaks English well but doesn't know not to take the question too literally. Outside of North America there are some alternative phrases used to perform the same function. In England "(Are) you alright?" is the most popular one. This one is confusing for a North American, as to us that question indicates that the person asking it believes that something is wrong with us.