Economic term for relation between drug and companion diagnositic I'm looking for economic terminology which must exist, although I don't know what it is.  (I want to look up articles on a particular situation involving two real-world companies.)

Here is the situation:  Company A is developing a diagnostic test which will warn of a particular type of deadly antibiotic resistance.  Company B is a pharmaceutical company developing a drug to treat that kind of resistance.  

Is there an economic terms that describe concepts relevant to this situation?   The important features are that 

1)  Product B will never be bought without product A.
2)  Customers will only buy A with the intention of possibly buying B.
3)  Product B will certainly sell at a very high price if product A works perfectly, because A will identify those patients for which B is life-saving.  A deserves some of this return, but the many customers buying A each will have only a low-probability of being one of the few to benefit.

Similarly, one could imagine a related case that there are exactly two bicycle wheel manufacturers, and by law A can only sell front wheels and B can only sell back wheels.  There will be some sort of odd price hostility between A and B, because the two products are each useless without the other.  The natural thing to happen is for the producers A and B to merge, although wrangling about the terms of a merger may make this impossible. 

In my real-world case the cognizant shareholders of A should oppose any buyout by B at anywhere near current market prices, because A's technology will extend to many many other applications.
Product A and B are perfect complements. As the Wikipedia entry states:


  A perfect complement is a good that has to be consumed with another good. [...] One example is a left shoe and a right; shoes are naturally sold in pairs, and the ratio between sales of left and right shoes will never shift noticeably from 1:1, even if, for example, someone is missing a leg and buys just one shoe.


The example of the shoe matches the one of the bicycle you give.

Additionally, the two goods do not need to have a symmetric degree of complementarity. Again, quoting Wikipedia:


  In the case of video games, a specific video game (the complement good) has to be consumed with a video game console (the base good). It does not work the other way: a video game console does not have to be consumed with that game.


So, for example the base good can be the diagnostic and the complement is the drug.