Immunoglobulins (Blood)

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. 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.