Mental Health diagnosis code question

Here's a question for the coders out there - patient with an established diagnosis of bipolar presents for scheduled psychotherapy. Sessions focuses on reducing patient's anxiey due to family stressors - do you code the chronic condition primary (bipolar), or do you code the dx treated at that session primary (anxiety)? Curious to hear your responses / see any guidance from CMS. Thanks.

re: Mental Health diagnosis code question

I would think that you would use the DX thats being treated at the session and code the bipolar as the secondary DX.