Test Background IgG antibody levels to Streptococcus pneumoniae are requested as part of immune deficiency screen for patients with recurrent or opportunistic infections, and should be done alongside tetanus toxoid antibodies. This test measures antibodies to Pneumovax serotypes as occurring in vaccine containing a mix of 23 capsular serotypes of Streptococcus pneumoniae (polysaccharide antigens). Antibodies measure the T-cell independent immune response. However, this response requires a mature immune system, hence normal values are age related and the test is not indicated in patients less than 2 years of age. A good overall response may not indicate protection to individual serotypes.