Identification and quantification of hemoglobins A2 and Barts with an enzyme-labeled immunosorbent assay

The presence and quantity of hemoglobins Barts and A2 in hemolysates from normal donors and individuals with alpha- and beta-thalassemia trait, respectively, were determined with an enzyme-labeled immunosorbent assay (ELISA). This technique requires the incorporation of monospecific antisera capable of specifically reacting only with these hemoglobins, e.g., with the delta chain of Hb A2 and gamma 4 chains of Hb Barts. By the ELISA, the mean percentage of Hb Barts in hemolysates from normal persons and persons with alpha-thalassemia was 0.25 (SD 0.07) and 6.1 (SD 0.40), respectively. Corresponding values for Hb A2 in hemolysates from normals and persons with beta-thalassemia were 3.1 (SD 0.22) and 5.9 (SD 0.21), respectively. The results obtained by the ELISA procedure were in good agreement with those determined by radioimmunoassay or microcolumn chromatography. The ELISA technique is more sensitive and specific than biochemical assays currently used to measure these hemoglobins and can detect 250 ng of Hb Barts in 100 micrograms of hemoglobin or 50 ng of Hb A2 in 5 micrograms of hemoglobin.