bound/free ratio

in immunoassay
initialism: B/F
https://doi.org/10.1351/goldbook.09667
Amount of analyte bound by a label divided by amount of unbound (free) analyte
Source:
PAC, 2018, 90, 1121. 'Terminology of bioanalytical methods (IUPAC Recommendations 2018)' on page 1137 (https://doi.org/10.1515/pac-2016-1120)