The most abundant immunoglobulin in human serum is immunoglobulin G (IgG) (about 75% of the total). There are four subclasses (subtypes) of immunoglobulin G, IgG1, IgG2, IgG3, and IgG4, of which IgG1 accounts for approximately 60-65% of total immunoglobulin G, IgG2 approximately 20-25%, IgG3 6 %, and IgG4 4% of the total. The IgG1 and IgG3 subtypes bind the complement better than the other subclasses and in addition, IgG3 has a disproportionately large effect on serum viscosity.
The immune system's responses to the production of IgG antibodies against certain antigens result in a greater production of one IgG subtype and little or no production of the remaining subtypes. Therefore, some patients with normal levels of total IgG may have problems with pyogenic infections because they cannot produce IgG2 or combinations of IgG2, IgG3, and/or IgG4. Some clinically significant IgG subtype defects occur in patients with IgA deficiency.
The four IgG subclasses differ in the constant regions of their heavy chains. A patient may have a normal amount of total IgG but may have a significant decrease in one subclass. Deficiencies in the IgG1 subclass are associated with EBV infections, IgG2 with respiratory and bacterial infections, IgG3 with sinusitis and otitis media, and IgG4 with allergies, ataxia-telangiectasia, and respiratory infections.
Measurement of IgG1 assesses the T-cell response in patients with a low response to viral or bacterial antigens and immunodeficiency syndromes. IgG2 measurement is used to evaluate the presence of anti-lipopolysaccharide antibodies, respiratory infections, immunodeficiency syndromes, and in patients who show low response to carbohydrate antigens (Group A streptococcus and pneumococcus). The measurement of IgG3 is used for the evaluation of immunodeficiency syndromes and in both recurrent sinusitis and otitis media. The IgG4 measurement is used to evaluate respiratory infections, asthma, immunotherapy, and allergies.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.