From the Guidelines
IgG levels less than 9 and IgM levels less than 18 are not necessarily significant signs of infection or immune response, and may actually indicate normal or low immunoglobulin levels rather than infection. These values can be considered within normal reference ranges for many laboratories, though specific reference ranges can vary between testing facilities 1. When interpreting antibody levels, it's essential to consider the clinical context, including symptoms, exposure history, and other laboratory findings. The timing of testing is also crucial, as IgM appears early in infection (within 1-2 weeks) and then declines, while IgG develops later and persists longer. Some key points to consider include:
- Low immunoglobulin levels might indicate immunodeficiency rather than infection, while elevated levels typically suggest active infection or immune response 1.
- For accurate assessment, antibody levels should be interpreted by healthcare providers who can consider the specific reference ranges of the testing laboratory, the patient's clinical presentation, and potentially order follow-up testing if needed.
- Single antibody measurements provide limited information, and paired samples showing a rising titer are more diagnostically valuable for confirming recent infection.
- The diagnosis of antibody deficiencies involves measuring levels of various immunoglobulin isotypes (IgG, IgA, IgM, and possibly IgG subclasses) in serum, as well as a measure of function or specific antibody production 1.
From the Research
IgG and IgM Antibody Levels
- The provided antibody levels are IgG less than 9 and IgM less than 18.
- According to the study 2, a patient with antiglomerular basement membrane disease had IgG levels of 9, which was considered low.
- Low IgG levels can be associated with immunosuppression, as seen in patients taking prednisone and azathioprine 2.
- The study 3 found that immunosuppressive drugs can decrease B-1a lymphocytes and suppress antigen-specific IgM antibodies.
Clinical Significance
- Low IgG and IgM levels may indicate a compromised immune response, making patients more susceptible to infections 2, 3.
- The study 4 reported a case of hepatitis E infection in a patient with rheumatoid arthritis and autoimmune hepatitis, where the patient had a significant increase in liver enzymes and was positive for anti-nuclear autoantibodies.
- Elevated IgM levels can be associated with autoimmune diseases, such as primary hyper-IgM syndromes 5.
- The detection of IgM antibodies to Chlamydia and Mycoplasma pneumoniae can indicate an aggravation of intracellular infections, possibly due to immunosuppressive therapy 6.
Immune Response
- The immune response to infections can be affected by immunosuppressive therapy, leading to decreased antibody production 3.
- The study 5 discussed the role of specific immunoglobulin isotypes in human autoimmune disease, including the presence of polyclonal gammopathy in systemic autoimmune diseases.
- The detection of antibodies to Chlamydia and Mycoplasma pneumoniae can accompany increased total immunoglobulin IgM and IgG in blood serum 6.