How do therapists characterize personality types?

This is a great question, and I am happy to have the opportunity to explain my approach. When I am determining what type of personality a client has, I take my time and really absorb their lens/ point of view to themselves and others. Determining a personality type takes some time getting to know the person, and building rapport. After taking time to get to know them, and learning about their view they have of themselves and others, it is important to pick-up on more specific personality traits, which comprehensively contribute to a personality type. Clinicians, including myself, often witness certain traits that are enduring and consistent, which indicate a type of personality. For example, if a therapist is noticing that a client is exhibiting traits of organization, needing to be on time, planning, and perfectionism, these traits contribute to the "type A personality". In addition to utilizing clinical judgment, clinicians often use personality assessments and follow the guidelines of the DSM-5/ ICD-10. 

That's a great question. There is such a wide range of ways to define "personality" that it is difficult to identify specific characteristics that are used to identify personality types.

That being said, some clinicians will use standardized tests (or assessments) to assess a client's type of personality. While these tests can't tell us everything about a person, they can help us understand where we are within larger groups of different personality styles.

Some counselors will also use a diagnostic tool (like the DSM or ICD) to help a client understand a diagnosis that is related to a personality disorder.

In my therapy practice I avoid characterizing people except for whether or not they are self-harming or a risk to harm other people.

As long as someone is sincerely trying to know more about themselves my work is help the person clarify who they really are and how their true self may be quite different than the life the person created for themselves, based on satisfying other people's standards.

In broad terms, personality disorders have stock characteristics which change very minimally over time instead of  uniqueness  which constantly flows and changes with circumstances over time.