To confirm a clinical impression or make a diagnosis. To screen for occult disease. To follow the course of a disease or a treatment. To confirm a clinical impression. Decide how to manage the patient.
Blood tests adjust the probability of a given diagnosis up or down depending on the result.
Rarely are they pathognomonic. Must be interpreted along with case history and physical findings. 2 SD in an undiseased population. Is elevated a high percentage of patients with active sarcoidosis. Not pathognomonic of the disease.