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 ...

The other issue with quantitative sAg is eligibility for clinical trials and potentially to be able to use the new GSK drug Bepe in the near future. Patients with s levels below 1,000 are much more likely to clear their surface antigen than those with levels above 1,000.