The blood tests are to reveal the state of her blood cells in relation to massive weight loss. Anorexia will result in losses of minerals and proteins etc necessary for a healthy body. Some of these can be substituted to keep her going until a treatment for her overall condition has been decided upon. Anorexia nervosa is the term used when it has become a psychiatric problem. Being anorexic can be normal. In cases were a person has an ongoing illness it is quite common for that person to go off their food and even loss weight. However, when it becomes life threatening and out of control the real help will come from the psychiatric department. Good luck.:)
There is not a specific blood test that can determine anorexia. But her dr has probably ordered a series of blood tests and put together, the results can help determine if she does indeed have anorexia or if there is some other underlying problem that no one knew about.
No you cannot tell by a blood test if she has anorexic.