**4.2 Serology**

As described above, the only valuable serological marker is the serum IgG4 level [17]. However, its performance in the diagnosis is variable: it can be increased only in type 1, not in type 2. Other unspecific autoantibodies have low sensibility in AIP and are not used routinely. Sometimes, IgE and peripheral eosinophils can be increased. If altered, they help in the diagnosis; if not, they have no value in excluding it.
