Laboratory investigations - immunoglobulins

Role

Quantitative immunoglobulin testing (IgG, IgA, IgM, and sometimes IgE) assesses humoral immune competence and screens for both immunodeficiency and paraprotein-producing disease
Interpreted alongside the clinical context - infection history for suspected immunodeficiency, or unexplained anaemia/renal impairment/bone pain for suspected paraproteinaemia

Low immunoglobulins - primary antibody deficiency (e.g. common variable immunodeficiency), secondary causes (nephrotic syndrome - urinary loss; protein-losing enteropathy; some malignancies/medications)
Raised immunoglobulins - polyclonal (chronic infection/inflammation, liver disease) vs monoclonal (a paraprotein - suggests a plasma cell disorder, from MGUS to multiple myeloma)
Elevated IgE - atopic disease, and markedly elevated levels seen in some primary immunodeficiencies (e.g. hyper-IgE syndrome) and parasitic infection

Serum protein electrophoresis + immunofixation identifies and characterises a suspected monoclonal band; quantitative immunoglobulins alone cannot distinguish polyclonal from monoclonal elevation
Recurrent sinopulmonary bacterial infection + low IgG (+/- low IgA/IgM) should prompt formal immunodeficiency workup, including vaccine response testing

Primary antibody deficiency - immunoglobulin replacement therapy (IVIG/subcutaneous) for significant deficiency with recurrent infection
Monoclonal gammopathy - further workup (bone marrow, skeletal survey/imaging, free light chains) to distinguish MGUS from myeloma or another plasma cell disorder

Common variable immunodeficiency, multiple myeloma/MGUS, nephrotic syndrome, chronic infection/inflammation

MGUS (monoclonal gammopathy of undetermined significance) requires long-term monitoring given a small but persistent annual risk of progression to myeloma or another lymphoproliferative disorder

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.