Economic term for relation between drug and companion diagnositic
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.