The inhibition of the primary interaction between 125I-labeled human hemoglobin and rabbit anti-human hemoglobin sera: a sensitive radioimmunoassay technique.

A rapid and sensitive radioimmunoassay technique for hemoglobin based upon a modification of the Farr test is described. Since hemoglobin is soluble in ammonium sulfate whereas antibody is precipitated, the amount of free and antibody-bound radiolabeled human hemoglobin can be quantitatively measured after ammonium sulfate precipitation. Nanogram quantities of hemoglobin can be detected by the addition of unlabelled human hemoglobin to the antiserum before the labeled hemoglobin, thus establishing a competition reaction between labeled and unlabeled antigen for antibody. If sufficient quantities of unlabeled human hemoglobin are present, all of the antibody combining sites become saturated and the primary interaction between 125-I-labeled hemoglobin and antibody is completely inhibited. The method can be employed to discriminate various normal human hemoglobins, non-human primate hemoglobins as well as sickle-cell hemoglobin (HbS). Other possible applications of the technique are discussed.