When would you consider quantification of hepatitis B surface antigen as part of the treatment decision making process?  

I rarely send it but others use it religiously. If patient wants to know how likely he/she will be able to stop antiviral treatment after a certain period of time, HBsAg titer can provide a guesstimate e.g fairly likely if HBsAg levels <100 IU/m but if > 1,000, extremely unlikely. But you can ...