From wiki - Jain KK. Textbook of Personalized Medicine, Springer, 2009.
...Moreover "theranostic" is confusing and not understood by most people and should be deleted from the vocabulary. There is no difficulty in describing this concept without using a special term. Diagnostics used to guide therapeutics are also called “companion diagnostics”. If one has to use a single word to describe a test linked to therapy, one can use "pharmacodiagnostic", which is more appropriate and easy to understand.