As defined by the oldest European Institute of Trichologists in United Kingdom (establised 1902) a Trichology specialist or Trichologist must be fully capable in providing diagnosis and expert advice on the treatment or another hair restoration solution for:

Even though Trichologists are not always qualified for medical practice, they are highly trained and specialised in their discipline. During initial consultation the professional Trichologist must identify and select from the whole variety of possible disorders and diseases one or more specific to particular case. Diagnosis should be based upon scuh factors as ongoing hair loss and growth characteristics, different external defects and irregularities of hair, scalp condition, etc., or, in other words, the specific person overall health and hair condition identification. In any case, this is always done with the help of microscopic evaluation. After an identification (diagnosis) performed Trichologist shall provide a detailed explanation of research results and advise on the proper solution to the problem. During consultation you may be asked a series of questions about yourself, hair problems of your family members and relatives, lately underwent illnesses and diseases, physical or emotional injuries, medication prescribed and general health status, hair care and maintenance, etc. All this might be necessary to collect history of disease or anamnesis (abbr. Hx) in order to determine the potential start of particular hair problem - was it influendced by some of the internal or external factors. etc. Also typically a visual inspection of the hair loss or hair thinning form should be performed as well as scalp condition assessment - is it flaky, oily, itchy, scratchy, reddish, etc.; evaluation of the status of the hairs - whether they look healthy and shiny, or are they damaged and splitted, etc. Additionally, nail, teeth and eye-lid condition may be of interest, as their structural changes may have the same basis as for hair. Apart from microscopic studies, Trichologist, based on specific evidence or certain uncertainty about the current health status, may suggest some more tests to be performed, like blood biochemistry, endocrine, gastro-intestinal system tests, etc. For example, for most hair growth disorders, their enhanced breakage and  signs of loss, a full blood biochemical tests may be advised. These tests will show a body mineral metabolism state, including trace elements, vitamins, aminoacids, heavy metals. etc. The test results may suggest on the products to be entered into the daily diet or, vice versa, their consumption to be reduced, etc. in order to stop or prevent hair loss. As you know the hair is a blood product, and hair follicle activity depends on human body health status. In general a lack or excess of protein, certain trace elements (iron, copper, zinc, silicon, etc.), vitamins (especially vitamin A, C and B group) may promote a greater variety of hair problems. Quite often the hair and scalp diseases and hair loss may be caused by emotional stress, and in such cases a person might be anxious and frustrated, so good Trichologist must be a good Psychologist as result will depend on a specific person mental state and Trichologist-Patient mutual trust.