The determination of the amount of phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit alpha isoform:phosphatidylinositol 3-kinase regulatory subunit alpha complex in a sample. The trait is phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit alpha isoform:phosphatidylinositol 3-kinase regulatory subunit alpha complex measurement (Experimental Factor Ontology id EFO_0020636).