Do titers fluctuate? if so, why and to what degree?

Yes.: Any lab value goes up and down and is never the same twice. How high or low is another story. It depends on what is being measured, as, well as why it's being done in the first place. No lab result can be interpreted exactly without knowing the history and symptoms of the person tested. There are also "lab errors," improper preparation for testing, and other reasons for inaccurate results.