My son is 4 years old. he has skin allergy. immunoglobulin e test. result shows 429.7 iu/ml. can this be treated. should we need to do any other test?

Yes: Elevated serum IG e is a diagnostic marker of immediate-type allergic reactions. Normal serum ige levels are given by the manufacturer as <10 iu/ml for age 0–3 years. Your son's level is above normal range. On a top of it he is symptomatic (skin allergy). Next step to do is a skin prick test to identify what specific allergens he is sensitized to - allergy/immunology referral. Than avoid offenders.