Serum IgG levels reduced by more than 2 SDs below the mean, accompanied by deficiencies in IgA and/or IgM, suggest common variable immunodeficiency.

Laboratory studies show low levels of serum IgG and IgA with normal or elevated levels of IgM, decreased IgG antibody responses, and variable T-cell defects. Patients with one of the hyper-IgM syndromes, X-linked or autosomal recessive, have a deficiency of IgG and IgA. Peripheral blood CD19 + B-cell counts are commonly less than 0.1%. Serum IgG levels are usually less than 200 mg/dL, and IgM and IgA levels are less than 20 mg/dL. Laboratory findings include profound hypogammaglobulinemia and extremely low to absent circulating B cells. The diagnosis of X-linked agammaglobulinemia or the rarer autosomal recessive form of agammaglobulinemia is usually made in the first few years of life due to family history or recurrent sinopulmonary infections. Most infants with transient hypogammaglobulinemia of infancy achieve normal levels of serum IgG by the age of 2 years however, few continue to have low levels of IgG until 5 or 6 years of age. Laboratory findings include IgG levels less than 2 SDs below the mean for age, normal B-lymphocyte numbers, and normal or near normal IgG antibody responses to vaccines. Hypogammaglobulinemia in infants younger than 2 years may suggest transient hypogammaglobulinemia of infancy. IMMUNOLOGIC CONDITIONS WITH REDUCED IgG LEVELS In the first year of life, premature infants should be compared with infants of similar gestational age. An immunoglobulin level within 2 SDs of the mean for age-matched controls is considered normal. Correct interpretation of IgG levels relies on reference to age-matched controls ( Table 1). However, because immunoglobulins and antibodies are rather resistant to deterioration, these conditions, although desirable, are not mandatory. 3 Serum samples should ideally be stored at 2☌ to 8☌ or frozen at −15☌ to −20☌ if the assay is delayed. Monoclonal immunoglobulins or heterophile antibodies (usually anti–goat immunoglobulins) may elevate levels of detected immunoglobulins. However, substances other than antigen-antibody complexes in solution can increase background light scatter, leading to incorrect results. Nephelometry is an automated and rapid method used to measure serum immunoglobulin levels it relies on the light-scattering properties of antigen-antibody complexes. VARIABLES AFFECTING MEASUREMENT AND INTERPRETATION

Superliminal igg