Well, your scenario about a new patient visit with documentation of two of three areas (past medical and social) qualifies as relevant PFSH.
How it functions: There are three levels of PFSH, which are none, pertinent, and complete. With no PFSH, you can reach only a detailed history level, which is associated with 99203 (Office or other outpatient visit for the E&M of a new patient). You may see this level for some surgical patients; however most likely not for complex cases such as patients thinking about bariatric surgery.
What's relevant: For PFSH portion of detailed level of history, you need a pertinent PFSH, which is 'a review of the history area (s) directly related to the problems identified in the HPI.
According to the guidelines, a pertinent PFSH calls for documentation of atleast one specific item from any of the three PFSH areas. CPT needs a minimum of a detailed history for 99203.
Complete PFSH: To go beyond that reach a thorough level of history (required for 99204-99205), documentation must include a complete PFSH. Whether you must have documentation of two areas or three areas for a complete PFSH depends on the type of service. As per the guidelines, for a new patient visit, you need one specific item from each of the three areas. In comparison, you'd need items from only two of the three areas for an established patient office visit.
Remember: If you figure out that a surgeon is consistently leaving out any of the elements in the PFSH, the compliance team may want to consider planning a session with your doctors to go over documentation requirements for E/M services.
For more on this and other evaluation & management guidelines, turn to a medical coding guide like http://www.supercoder.com/