The determination of the ratio of Hemoglobin A2 compared to total Hemoglobin present in a sample. The measurement may be expressed as a ratio or percentage. [ NCI ]. The trait is Experimental Factor Ontology identifier EFO_0009212 (Hemoglobin A2 to Total Hemoglobin Ratio Measurement). Also known as: HGBA2HGB, Hemoglobin A2/Total Hemoglobin, Percent Hemoglobin A2.