immunology allergic disorders
Selective Antibody Deficiency With Normal Immunoglobulins (SADNI)
Diagnosis of SADNI
Usually normal immunoglobulin levels (IgG, IgA, IgM, and IgG subclasses) Deficient or absent response to polysaccharide vaccines Because healthy children < 2 years can have recurrent sinopulmonary infections and weak responses to polysaccharide vaccines, testing for SADNI is not done unless patients are > 2 years. Then, levels of IgG, IgA, IgM, and IgG subclasses and responses to vaccines are measured. Laboratory testing shows a deficient response to polysaccharide vaccines (eg,pneumococcal vaccine) and a normal response to protein antigens (eg, tetanus toxoid, diphtheria toxoid) and/or conjugate vaccines (eg,Haemophilus influenzaetype b). Testing usually involves giving the 23-valent polysaccharidepneumococcal vaccine(PPV), with quantitative measurement of antibody response; most clinicians assess response to 12 to 14 serotypes. Ideally, titers are done by the same laboratory both before and after vaccine administration. Response to each serotype is characterized by the degree of rise in titer and whether the titer is considered protective, defined as an antibody level ≥ 1.3 mcg/mL (1.3 mg/L). A normal response to PPV for children age 2 to 5 years is defined as protective antibodies to ≥ 50% of the serotypes tested, with at least a 2-fold increase in the titers; patients 6 to 65 years should have protective antibodies to ≥ 70% of serotypes. Patients with abnormal results can be classified phenotypically as follows ( Diagnosis reference ): Memory phenotype: Normal initial response to PPV23, which is lost within 6 months. Mild phenotype: Multiple serotypes (> 50% for children 2 to 5 years or > 30% for patients 6 to 65 years) without protective titers or without a 2-fold increase in titers Moderate phenotype: Protective titers to ≥ 3 serotypes but fewer than the expected number for their age Severe phenotype: Protective titers to ≤ 2 serotypes, and the titer, if present, tends to be low (< 1.3–2.0 microg/mL [< 1.3–2.0 mg/L]). Family members of known patients do not need screened unless they manifest a similar clinical picture. 1.Orange JS, Ballow M, Stiehm ER, et al: Use and interpretation of diagnostic vaccination in primary immunodeficiency: a working group report of the Basic and Clinical Immunology Interest Section of the American Academy of Allergy, Asthma & Immunology.J Allergy Clin Immunol130 (3 Suppl):S1–S24, 2012. doi:10.1016/j.jaci.2012.07.002 