Infection and immunity

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This section deals with clinical conditions associated with infection and immunity which are covered by the Immunology department. For each clinical condition, the relevant immunological tests are listed together with a short explanation of their use.

Please phone Immunology Clinical Staff (ext 66468) to discuss the investigation of recurrent unusual infections.

Primary immunodeficiency (PID) can cause preventable death or morbidity. Consider PID in patients with:

  • recurrent infection
  • severe infection
  • infection refractory to antibiotics
  • unusual infection

Don’t forget that PID can present in childhood and adulthood as well as in infancy.

Guidelines for testing are available from the UK Primary Immunodeficiency Network (UKPIN)

Patient information is available from the Primary Immunodeficiency Association

Primary immunodeficiency

The following panels of tests are available for investigating patients:

Background

Grouping is frequently based on the specific fault in the immune system. This may include:

  • B Cell antibody deficiency causes mainly recurrent bacterial infections
  • T cell deficiency causes viral, protozoal and fungal infections
  • Combined T and B cell deficiencies
  • Defective phagocytes
  • Complement deficiencies cause mainly bacterial infection

There are no ‘screening tests’ for immune deficiency. In cases with recurrent bacterial infection it may be sensible to start by measuring immunoglobulins, but we advise discussing individual cases early on.

Hereditary angioedema

Relevant immunological tests:

Recurrent abdominal pain and/or deep subcutaneous swellings without urticaria (particular occurring after minor trauma), often with family history, may indicate HAE. C4 and C1 inhibitor will be low.

Uncommonly there may be normal C1INH level with defective function. If C4 is very low without other explanation and C1INH normal, C1INH function will be measured.

Secondary immunodeficiency

Relevant immunological tests:

Secondary causes of immunodeficiency are more common than primary causes and levels of immunoglobulins might reflect decreased production (eg. lymphoproliferative disorders, drugs) or increased losses (nephritic syndrome).

In HIV infection the CD4 count is used to monitor progress of disease and inform treatment decisions. Other acute and chronic diseases affect CD4 counts.

In HIV infection they are best done at the same time of day each time and avoiding acute ill health. They should never be done as a substitute to HIV antibody testing to diagnose HIV infection.

Guidelines and information on CD4 counts are available from Aidsmap.

Patient information

Additional patient information is available from:

Acquired C1 esterase inhibitor deficiency

Relevant immunological tests:

Consumption/inactivation of C1INH may occur in SLE and lymphoproliferative disease. This may lead to episodes of angioedema as with the inherited form. C1q is low in acquired C1INH deficiency but usually normal in HAE.

TB exposure: Quantiferon

Relevant immunological tests: Gamma Interferon (Quantiferon)

This test measures gamma interferon produced by T cells in response to M. tuberculosis peptides.

The test is used to help diagnose latent TB infection and is indicated in individuals with a positive delayed hypersensitivity skin test.

The test may produce indeterminate results in patients with active TB and in immune deficiency states.

 

(Last updated October 8th 2014)