I consider agnosticism to be a response to a completely different question than responses about belief like atheism, theism, deism, pantheism, etc.
To me, terms like "theist" and "atheist" are statements about belief in deity/ies. In contrast, the term "agnostic" is a statement about knowledge of deity/ies: it's the position that the existence or non-existence of God/god/gods is unknowable, either merely currently (weak agnosticism) or for all time (strong agnosticism).
Because of this, I think that a person can simultaneously be an agnostic and an atheist (e.g. "I don't think we can ever know for sure, but I don't believe God exists") or agnostic and theist (e.g. "I believe in God, even though He tests our faith by not revealing Himself").