Allergies – Diagnosis and treatment – Mayo Clinic

Specific IgE (sIgE) blood testing, commonly called radioallergosorbent test (RAST) or ImmunoCAP testing, measures the amount of allergy-causing antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. A blood sample is sent to a medical laboratory, where it can be tested for evidence of sensitivity to possible allergens.

https://www.mayoclinic.org/diseases-conditions/allergies/diagnosis-treatment/drc-20351503