Immunoglobulins

Low IgA ( <0.5 g/L): Selective IgA deficiency occurs in 1:600 of the population. Most are asymptomatic and do not require referral, however those with recurrent infection, allergy or autoimmune disease may need to be seen. http://piduk.org/static/media/up/PIDUKSelectiveIgA.pdf

Low IgM: Commonly occurs in infancy or >60 years of age. May occassionally be an indicator of immunodeficiency or haematological disorders.However if general assessment and frequency/severity of infections are unremarkable, immunology referral is unlikely to be helpful. Serum protein electrophoresis and urinary Bence Jones protein should be considered. 

Low IgG / Low levels of several Ig classes: Please refer to immunology with details of infection history.

High IgA,IgM,IgG: Check serum protein electrophoresis for a monoclonal band and urine for Bence Jones protein.

If no band (polyclonal rise): consider any possible chronic inflammatory conditions ( including liver disease and malignancy), acute or chronic infection (including HIV) and refer appropriatley.

If a paraprotein band is detected , consider referral to haematology https://b-s-h.org.uk/guidelines/guidelines/investigation-of-newly-detected-m-proteins-and-the-management-of-mgus/