One or multiple immunoglobulins capable of binding to human antibodies from immunoglobulin class G (IgG) that are fixed to red blood cell antigens. This immunoglobulin, known as monospecific immunoglobulin G antihuman globulin (IgG AHG) is intended to be used in immunohaematological testing of a clinical specimen to detect red blood cell sensitization by human IgG, using an agglutination technique.