Utility of the antibody response to a conjugated Haemophilus influenzae type B vaccine for diagnosis of primary humoral immunodeficiency

Antibody response to an Haemophilus influenzae type b (Hib)-conjugated vacc ine was studied in 59 healthy adults (mean age: 32 yr) and 22 patients with humoral immunodeficiencies (mean age: 32 yr) to determine its usefulness i n the diagnosis of defective antibody formation. Twenty of the healthy adul ts and nine of the patients were also immunized with a pneumococcal vaccine , Serum specific antibodies were measured by ELISA. Adequate response to bo th vaccines was defined using the lower limit of the two-tailed 90% probabi lity interval of postimmunization specific IgG of the healthy adults. By us ing this cutoff, responders were considered to be those with an absolute in crease in anti-Hib IgG titers higher than 2.28 mu g/ml, and in anti-Strepto coccus pneumoniae IgG higher than 395 arbitrary units/ml. With these criter ia, 85% (50 of 59) of the healthy adults responded with anti-Hib IgG and 75 % (15 of 20) with anti-pneumococcal IgG. All healthy adults receiving both vaccines responded to at least one. None of the patients with humoral immun odeficiencies responded to either vaccine. Evaluation of the antibody respo nse to both the Hib and pneumococcal vaccines may facilitate the diagnosis of humoral immunodeficiency and selection of patients to receive immunoglob ulin therapy.