Table I.

Terminology of Analyte Forms in Biological Fluids and Assay Types

Term	Definition
Free drug, mAbfree (interchangeable with “active mAb”)	The sum of bivalent and monovalent unbound forms of mAb
Partially free mAb	mAb with one site (monovalent) bound to L and the other site unbound
Active mAb (interchangeable with “free mAb”)	The sum of both unbound forms of mAb (bivalent and monovalent) that are able to bind to L to interfere biological actions of L
Bound mAb, mAbbound	mAb with both sites bound to L
Total mAb, mAbtotal	Sum of bound and free mAb (mAbbound + mAbfree)
Free target ligand, Lfree	Unbound L
Bound target ligand, Lbound	L bound to mAb
Total target ligand, Ltotal	Sum of bound and free (unbound) L (Lbound + Lfree)
Specific assay	Measures a known form(s) of the analyte. Example: the combination of the capture and the detection reagents is directed towards a unique epitope of L or mAb.
Generic assay	Measures a class of analytes with shared epitope recognized by the reagents; the exact measurements may include more than one analyte.
Non-inhibitory assay	The capture and/or the detection reagents are directed toward an epitope that is non-competitive to L (or mAb) of interest, thus no or minimal inhibition is observed from L (or mAb).
Inhibitory assay	The capture and/or the detection reagents are directed toward a competitive epitope of L (or mAb), which will inhibit the assay at an appropriate molar ratio.

“mAb” is defined as a monoclonal antibody therapeutic in the paper, “L” refers to the target ligand in circulation. For simplicity, L is treated as monovalent