The amount of a MHC class II histocompatibility antigen alpha chain DQA2 when measured in blood serum. The trait is level of MHC class II histocompatibility antigen alpha chain DQA2 in blood serum (Ontology of Biological Attributes id OBA_2040364). Also known as: blood serum MHC class II histocompatibility antigen alpha chain DQA2 amount.