Immunoglobulins (IgG, IgA, IgM)

Alternative name: IgG, IgA, IgM
Description: Immunoglobulin levels are essential only in investigations for immunodeficiency states and in suspected myeloma or related diseases where they should be carried out in conjunction with serum electrophoresis. Elevated levels of immunoglobulins may be of limited use in the differential diagnosis of some diseases e.g chronic liver disease. Primary biliary cirrhosis is characterised by raised IgM: IgG and IgA are raised in viral hepatitis, IgA in portal cirrhosis. Immunoglobulin measurements are a poor indicator of general inflammation.Patients with infections that are Severe, Prolonged, Unusual or Recurrent (SPUR) without known cause should be investigated for immunoglobulin deficiency. IgG deficiencies are usually associated with infections of this type. IgA deficiency is the commonest of the immunoglobulin deficiencies: the incidence is 1 in 500 of the general population, most of whom have no symptoms. The most common associations of IgA deficiency are with autoimmune disease particularly coeliac disease rather than infections.
Indication: Investigation of Ig deficiencies (primary or secondary) or myeloma (particularly secondary immuneparesis). Of limited use in investigation of other conditions e.g liver disease.
Interpretation: IgG, IgA and IgM samples are also run for electrophoresis even if this is not requested. All marked immunoglobulin deficiencies should be investigated. IgA deficiency is the commonest of the primary disorders. The incidence is 1 in 500 of the population but 30% are symptom free. Secondary immuneparesis is seen in bone marrow disorders e.g myeloma, nephrotic syndrome.
Sample: Serum Separator Tube (SST)
Assay details: Turbidimetry
Restrictions: Increased levels of lipids (lipaemia), haemoglobin (haemiolysis), or the prescence of icterus in the assay sample may affect the assay result.
Reference range: Adult ranges:
IgG: 6-16g/L
IgA: 0.9–4.5g/L
IgM: 0.5-2.0g/L
Assay range notes: Immunoglobulin levels are age related. In children, IgM IgG and IgA do not approach adult levels until around 1, 6 or 12 years respectively. IgG levels fall for the first 12 months of life as maternal IgG is cleared from the circulation. In all reports references are automatically corrected for age.
Turnaround time: 5 – 7 days
Analysing laboratory: Biochemistry