[How to diagnose a hereditary immunodeficiency?].

Efficient early identification of primary immunodeficiency is important for the patient prognosis and treatment. The first investigations need to be performed in case of severe, recurrent and/or unusual infections. Simple investigations like blood cell count, serum immunoglobulins level and postvaccination or post-infection serologies allow to direct the diagnosis. The medical history, the clinical examination and these laboratory investigations permit to realize more specific investigations according to the type of primary immunodeficiency suspected.