Suggest Confirmatory Test For Hyper-immunoglobulin Syndrome

my son is 4.5 yrs now and was diagonsed hyper ige syndrome almost a year back . he has eczema , have to moisturise his skin many times , his skin is very sensitive . other wise he looks and behave normally only . 2 yrs back his ige serum was 3000+ .since then he is getting better slowly . Never had any breathing problem or phnemonia . is there anyway i can it get it confirmed that he does not have hyper ige syndrome