Tests of immune function are carried out in the departments of Haematology and Biochemistry. Below is a brief description of the relevance of available tests. Most of the listed tests require serum from clotted blood unless otherwise stated. By clicking on the icon adjacent to the test further details may be obtained from the department which actually undertakes the analysis. 

Autoantibody Testing 

A number of diseases are due to the immune system failing to recognize the body’s antigens as “self” and mounting an immune response to host antigens. These “auto-immune diseases” may manifest themselves by the presence of auto antibodies and detection of these can be a valuable aid to diagnosis. If an autoimmune disease is suspected then a request for an “auto-immune screen” is appropriate. This screen comprises:

High levels of ANA are associated with connective tissue disease such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). An immunofluorescence technique is used to analyze ANA and the pattern obtained may give a clue to the target antigen and therefore the disease process involved (e.g. a homogenous pattern is associated with SLE) although this is not one hundred per cent reliable. Further analysis will be undertaken as necessary.

These are found in high titre in primary biliary cirrhosis (PBC) and also in lower levels in autoimmune hepatitis. (AIH). The two conditions are associated with different target antigens and further tests are available to distinguish between the two (see later – liver profile).

In high titre these are associated with autoimmune hepatitis but may also be found in low titre in PBC and infection.

These are found in ninety five percent of people with pernicious anemia (PA). A positive result should be followed by an Intrinsic Factor Antibody (IFA) test which, when positive, confirms a diagnosis of PA.

More specific autoantibody tests

These antibodies react with cytoplasmic constituents of neutrophils. There are two major patterns of clinical significance. C-ANCA, where the antigen is proteinase-3 (Pr 3), is strongly associated with Wegener’s Granulomatosis. P-ANCA, where the antigen is myeloperoxidase, is less specific and may be positive in a number of vasculitic conditions.

These are associated with arterial and venous thrombosis and may be found in isolation or in association with other diseases such as SLE. They may manifest as e.g. pulmonary emboli, thrombocytopenia or recurrent miscarriage. Lupus anticoagulant is a separate entity but the clinical significance is the same. Requests should be made for both tests. If a new positive result is obtained this should be confirmed after six weeks. If association with connective tissue disease is suspected ANA should also be requested.

This test should be requested where the ANA is positive and SLE is suspected. A positive result is associated with SLE.

These include antigens designated RNP, Sm, Ro (or SS-A), La (or SS-B), Scl-70, Jo-1 and histone each of which corresponds to a specific nuclear antigen. Antibodies to these specific antigens are associated with particular disease conditions (e.g. Ro and La with SLE or Sjogren’s syndrome and Jo-1 with polymyositis). 

Anti centromere antibodies are associated with a variant form of scleroderma termed the CREST (calcinosis, Raynaud’s, oesophageal dysmotility, sclerodactyly, telangiectasia) syndrome.

Anti GBM antibodies are associated with the glomerulonephritis of Goodpasture’s syndrome. They target a collagen constituent of the glomerular basement membrane and the resulting inflammation results in glomerular damage.

This is a compound test involving three antigens; M2, LKM and SLA/LP. Antibodies to M2 are strongly associated with PBC whilst antibodies to LKM and SLA/LP are associated with autoimmune hepatitis. 

RF is an antibody, which targets the tail portion (Fc region) of IgG with a resulting inflammatory response. It is found in a number of autoimmune and inflammatory diseases and also in healthy individuals, the frequency increasing with age. In rheumatoid arthritis the RF may be positive or negative although patients with severe disease tend to have higher levels. In such cases there is no value in serial monitoring of RF. CRP is a better indicator of inflammation.

These are found in males and females and may be implicated in infertility. They are also found in males after vasectomy.

Antibodies to thyroid peroxidase are found in Hashimoto’s thyroiditis, in about ninety per cent of cases, usually in very high levels. They are also found in up to three quarters of patients with Graves disease but at lower levels.

Transglutaminase is an enzyme involved in the processing of gluten found in wheat. Antibodies to this enzyme are found in patients with coeliac disease and also in some cases of liver disease. A positive screen will be confirmed by assay for endomysial antibodies which are more specific for coeliac disease. 

Immunochemistry

The three major immunoglobulin classes (IgG, IgA, IgM) form the basis of the humoral immune response. Their estimation is necessary in suspected cases of primary or secondary immunodeficiency. In acute and chronic inflammatory conditions levels may be polyclonally elevated. Such levels are rarely diagnostic but may offer supporting evidence. Analysis of immunoglobulin levels is essential in the investigation of lymphoid neoplasia. Electrophoresis, to determine the nature of immunoglobulins (i.e. polyclonal or monoclonal), is automatically carried out and need not be specifically requested. Monoclonal immunoglobulins may be associated with lymphoid neoplasia but small amounts of monoclonal protein are not unusual in elderly patients and may be benign. 

IgE is responsible for immediate type hypersensitivity e.g. hay fever. Tests for specific antibodies to a wide range of allergens are available but in order to limit the search relevant clinical data is needed although it is appreciated that detailed information may not always be available. 

The copper binding protein caeruloplasmin is reduced in most cases of Wilson’s disease and should be requested where this condition is a possibility.

The complement pathway comprises a series of proteins, C1 through to C9, which exist in blood in inactive form. Activation of C1 results in serial activation of the other components in a cascade fashion. The sequence may also be activated by the alternate pathway which starts with activation of C3. The estimation of C3 and C4 levels is useful in a pathological condition which may involve the complement pathway e.g. glomerulonephritis. Complement deficiencies are rare but in cases of persistent or unusual infections the estimation of CH50 is appropriate. This analyses the integrity of the entire classical complement pathway and requires a frozen specimen of serum.
The complement system is kept in check by a number of inhibitors. Deficiency of these is rare except for C1 esterase inhibitor, lack of which causes hereditary angioedema. Whilst this condition is not very common it is potentially fatal and treatable. An estimation of C1 esterase inhibitor, along with C3 and C4, is required for diagnosis.

These are proteins which show a tendency to precipitate just below body temperature with resultant complement activation which may manifest as renal or cutaneous vasculitis. Paired serum and EDTA specimens are required and need to be taken into warm syringes and transported warm to the laboratory. Contact the laboratory before taking blood. The request should include C3, C4, and immunoglobulins.