To Measure the Amount of a Small Drug (Hapten Sized)

To measure the amount of a small drug (hapten sized) that is in the patient's serum, can agglutination or precipitation reactions be performed, and if so, how?

A) Yes, agglutination inhibition can be performed as in PETINA.
B) Yes, precipitation inhibition can be performed as in PETINA.
C) No, since this molecule is so small it cannot be cross-linked and thus cannot be measured by precipitation or agglutination
D) Yes, although this molecule is too small for agglutination, it can be used in precipitation