From the Guidelines
Immunoglobulins (Ig) should be tested in patients with recurrent infections, suspected immunodeficiency disorders, or specific infections, particularly when evaluating immune function or suspected primary immunodeficiency disorders 1. When to test immunoglobulins is a critical decision in clinical practice, and it should be guided by the presence of specific clinical indications. These indications include:
- Recurrent infections, such as respiratory tract infections
- Suspected primary immunodeficiency disorders
- Evaluation of B-cell function
- Monitoring of immunoglobulin replacement therapy
- Diagnosis of multiple myeloma
- Assessment of maternal-fetal antibody transfer Testing for IgG, IgA, and IgM can provide valuable information about a patient's immune status, and the choice of which immunoglobulin to test depends on the clinical context. For example:
- IgG testing is particularly useful for evaluating chronic or recurrent infections
- IgM testing is useful for detecting acute infections
- IgA testing is important when assessing mucosal immunity or investigating IgA deficiency in patients with recurrent respiratory or gastrointestinal infections It is essential to consider age-specific reference ranges when interpreting immunoglobulin levels, as values can vary significantly between infants, children, and adults 1. Abnormal results should prompt further investigation with more specific testing, such as immunoglobulin subclass analysis or specific antibody responses to vaccines. However, IgG subclasses should not be checked routinely in immunodeficiency evaluation, as the connection of IgG subclass deficiency to recurrent infections is controversial 1.
From the Research
Immunoglobulin Testing
Testing for immunoglobulins (Ig), including IgA, IgG, and IgM, is crucial in various clinical scenarios. The following are instances when such testing is warranted:
- Recurrent respiratory tract infections: Patients experiencing recurrent infections, particularly those caused by agents of low virulence, should undergo immunoglobulin testing to rule out immunodeficiency syndromes 2.
- Suspected immunodeficiency: Individuals with a history of recurrent infections or infections caused by opportunistic pathogens may benefit from immunoglobulin testing to diagnose conditions like common variable immunodeficiency (CVID) 2, 3.
- IgM deficiency: Patients with suspected IgM deficiency, characterized by low levels of serum IgM, should undergo thorough immunological evaluation, including specific antibody responses 4.
- Chronic or recurrent infections: Testing for IgG subclasses is recommended in patients with chronic or recurrent respiratory infections, as deficiencies in these subclasses can occur despite normal total IgG levels 5.
- Diagnostic workup: Quantitative serum immunoglobulin tests can help diagnose various conditions, including those causing excess or deficient levels of IgG, IgA, and IgM 6.
Clinical Considerations
When interpreting immunoglobulin test results, consider the following:
- Impaired specific antibody responses: Patients with IgM deficiency or CVID may exhibit impaired antibody responses to pneumococcal antigens, which can guide treatment decisions 4, 3.
- IgG subclass deficiencies: Deficiencies in IgG subclasses can occur in patients with recurrent infections, and testing for these subclasses can inform treatment strategies 5.
- Treatment monitoring: Immunoglobulin replacement therapy can increase serum IgG levels, but monitoring of IgM and IgA levels is also necessary, as these may remain diminished over time 3.