<prompt> In a 4-year old boy who has history of pyogenic infections by bacteria with polysaccharide-rich capsules, which of the following investigations should he done?IgA deficiencyIgG 1 deficiencyIgG2 deficiencyIgA and IgG2 deficiency  <response>: Ans. d. IgA and IgG2 deficiency Recurrent episodes of pyogenic infections by capsulated organisms are most commonly observed in patients with selective IgA deficiency and decreased IgA or IgG subclass levels especially IgG2. Specific Antibody Deficiency SAD patients generally present with recurrent upper andor lower respiratory infections due to an encapsulated organisms Streptococcus pneumonia, Haemophilus influenza, Branhamella catarrhalis, or Staphylococcus aureus. Frequent, recurrent episodes of otitis media are most commonly observed in patients with selective IgA deficiency and decreased IgA or IgG subclass levels especially IgG2. Specific Antibody Deficiency SAD Antibody deficiency against microbial polysaccharide antigens is a well-established clinical entity and has been referred to as either antigen specific antibody deficiency ASAD or specific antibody deficiency SADQ Frequent, recurrent episodes of otitis media are most commonly observed in patients with selective IgA deficiency and decreased IgA or IgG subclass levels especially IgG2 Q. Frequent nfections were repoed in 92 of patients with SAD sinusitis, 77; pneumonia, 42; otitis media,25; bronchitis, 28. 