Diagnostic Use
The immunoglobulins blood test is used to assess the immune system by measuring levels of key antibodies—IgG, IgA, and IgM—in the bloodstream. These immunoglobulins play distinct roles in immune defense: IgM is the first responder to infections, IgG provides long-term immunity and is the most abundant, and IgA protects mucosal surfaces such as the respiratory and gastrointestinal tracts.
Reduced IgG
Reduced IgG levels may be due to primary immunodeficiency (eg X-linked hypogammaglobulinaemia, common variable immunodeficiency, severe combined immunodeficiency) or secondary causes (e.g. multiple myeloma, medications including B cell depleting agents such as rituximab). The lower reference limit of IgG can be lower in adults age >70 years or current smokers however in these groups it is not expected to be lower than 5.8 g/L.
| Adult IgG < 1 g/L |
Patients with severe hypogammaglobulinaemia are at risk of life-threatening or severe infection. Please refer to Clinical Immunology service for further advice. |
| Adult IgG 1 – 3 g/L |
If there is no known cause, please investigate for secondary causes and consider a Clinical Immunology referral if no cause is identified. |
| Adult IgG 3 – 5 g/L |
If no cause is identified or there is recurrent, particularly sino-pulmonary infections or other features of an immunodeficiency, consider referral to Clinical Immunology service |
| Paediatrics <12 years (i.e. <95th percentile) |
If IgG levels are reduce and there is no known cause, consider a paediatric Clinical Immunology referral. |
Low / undetectable IgA
Selective IgA deficiency (i.e. normal IgG and IgM) is seen in approximately 1:400 people and can occur in otherwise well individuals. It may be associated conditions (e.g. coeliac disease, inflammatory bowel disease), and anaphylactic reactions to blood products (when IgA is absent) and rarely recurrent sinopulmonary infection.
Elevated IgA, IgM or IgG
Elevated immunoglobulin isotype levels may be polyclonal (eg in infection, autoimmune or non-immune liver disease or autoimmune diseases like Sjogren’s syndrome) or monoclonal. Serum protein electrophoresis to exclude a monoclonal gammopathy should be considered, particularly in patients with evidence of immunoparesis to at least one other immunoglobulin isotype or where IgG > 25g/L, IgA >10 g/L or IgM >10 g/L.
Note: Acute infection can transiently elevate immunoglobulin concentrations to values within the reference limits in immune compromised patients.
Serial monitoring of immunoglobulin IgG, A or M should ideally be done through the same laboratory. Inter-platform differences of up to 40% (for results at or below lower reference limit), 25% (for results within reference limits) and 15% (for results above upper reference limit) can be observed between laboratories using different platforms or assays. In patients with paraproteinemia, even greater between-method differences may be seen.
Reference Intervals
Tables: Serum Immunoglobulin Units : g/L
NB New paediatric ranges from 29/6/2018
IgG LEVELS:
| 0 – < 2 weeks |
3.0 – 13.7 |
| 2 weeks – < 6 weeks |
1.2 – 6.0 |
| 6 weeks – < 6 months |
1.2 – 7.0 |
| 6 months – < 12 months |
3.0 – 10.5 |
| 1 year – < 4 years |
3.0 – 11.2 |
| 4 years – < 10 years |
5.0 – 13.3 |
| 10 years – < 19 years |
6.0 – 15.0 |
| 19 years – < 70 years |
7.0 – 16.0 |
| > 70 years |
6.0 – 15.0 |
During the late stages of a normal pregnancy maternal IgG is transferred across the placenta and contributes significantly to the IgG measured in an infant’s first few months of life. In pre-term infants IgG levels at birth may be significantly reduced due to reduced maternal IgG transfer. In a normal healthy infant, production of IgG increases significantly during the first year of life.
IgA LEVELS:
| 0 – < 1 year |
0.09 – 0.39 |
| 1 year – < 3 years |
0.19 – 1.09 |
| 3 years – < 6 years |
0.29 – 1.69 |
| 6 years – < 14 years |
0.3 – 2.4 |
| 14 years – < 19 years |
0.4 – 3.1 |
| 19 years – < 70 years |
0.8 – 4.0 |
| > 70 years |
0.8 – 4.0 |
Maternal IgA is not transferred across the placenta during pregnancy therefore level of IgA is generally much lower at birth. Total IgA levels can remain undetectable in normal children up to the age of 7 months. The production of IgA takes longer to reach mature levels (compare with IgG and M which increase significantly during the first year of life), therefore IgA deficiency cannot be reliably diagnosed in children <5 years of age.
IgM LEVELS:
| 0 – < 2 weeks |
< 0.5 |
| 2 weeks – < 13 weeks |
0.1 – 0.7 |
| 13 weeks – < 1 year |
0.1 – 0.9 |
| 1 year – < 19 years |
0.4 – 1.8 |
| 19 years – < 70 years |
0.4 – 2.5 |
| > 70 years |
0.4 – 2.4 |
Maternal IgM is not transferred across the placenta during pregnancy therefore level of IgM is generally much lower at birth. In a normal healthy infant the production of IgM increases significantly during the first year of life.
Test Method
Principle: Immunoturbidimetric assay
Analysers: Roche Diagnostics Cobas c503
Reagents: IGA-2, IGG-2, IGM-2