Glossary for autoimmunity testing

The terminology of autoimmunity can be difficult. Below, we have compiled the most common words and expressions in this area and how they are to be interpreted.


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The strength of the bond between an antigen and an antibody.

A molecule (also called an immunoglobulin) produced by a B cell in response to an antigen. The binding of antibody to antigen leads to the antigen's destruction.

A substance or molecule recognized by the immune system. The molecule may be from a foreign material such as a bacterium or virus, or from the same organism (one's own body), in which case it is called a self antigen.

Antigen-presenting cell
A cell that displays an antigen with an MHC molecule on the cell surface.

Antiphospholipid syndrome (APS)
Antiphospholipid syndrome (APS) is a systemic autoimmune disorder. In APS, the organism produces autoantibodies against phospholipids, major components of every living cell membrane. Symptoms of APS are venous or arterial thromboses, habitual abortion, thrombosis, foetal loss and thrombocytopenia. Various neurological disorders (excluding stroke) are also possible.

Programmed cell death (suicide)

Autoimmune hepatitis
A genetic predisposition or acute liver infection can lead to an immune response and to the production of autoantibodies against liver structures. Autoimmune hepatitis can develop cirrhosis.

The healthy human body is equipped with a powerful set of tools for resisting the onslaught of invading microorganisms such as viruses, bacteria and parasites. Unfortunately, this set of tools, known as the immune system, sometimes goes awry and attacks the body itself. These misdirected immune responses are called autoimmunity. It can be demonstrated by the presence of autoantibodies or T lymphocytes reactive with host antigens.

The overall strength with which a multivalent antibody binds with a multivalent antigen.



B cell
A type of lymphocyte, which is an immune system cell. Among its many roles, the B cell produces antibodies that bind antigens.

Barley is a common staple in human and animal diets. Part of the grass family, barley grows in over 100 countries and is one of the most popular cereal crops, surpassed only by wheat, corn and rice. Although barley is fairly adaptable and can be grown in many regions, it is a tender grain and care must be taken in all stages of its growth and harvest.

A systematic error that leads to results that do not represent the true findings.



Coeliac disease
Coeliac disease is an autoimmune disorder of the small intestine that occurs in genetically predisposed people of all ages from middle infancy onward. The lifelong intolerance to gluten leads to damage in the gastrointestinal tract. The consequence is the malabsorption of nutrients. Only a gluten-free diet relieves the patient from suffering a variety of symptoms. Symptoms include chronic diarrhoea, failure to thrive (in children) and fatigue. However, these may be absent, and symptoms in other organ systems have been described. The disease is more common in industrial countries and regions such as Europe, Russia, the Mediterranean countries, the Americas, South Africa, India, Australia and New Zealand.

Churg-Strauss syndrome
Eosinophilia and granulomatous inflammation of the respiratory tract with necrotizing inflammation of the small to medium-sized blood vessels; associated with asthma and eosinophilia.

Reagent formed by the covalent binding of two molecules, e.g. fluorescein bound to an immune molecule.

Connective tissue diseases (CTD)
Connective tissue diseases are a group of rare systemic autoimmune diseases affecting the connective tissue of the body. This group includes systemic lupus erythematosus (SLE), Sjögren´s syndrome, scleroderma, limited systemic sclerosis (CREST), poly-/dermatomyositis and mixed connective tissue disease (MCTD). 





European Autoimmunity Standardization Initiative

The ability of an intervention to achieve the desired results under usual conditions.

The ability of an intervention to achieve the desired results under ideal conditions.

Enzyme immunoassay

Enzyme-linked immunosorbent assay
ELISA is a method of quantitative analysis in which one of the reagents is labelled with an enzyme, which may be an antigen or an antibody.
Usually, a microtitre plate is coated with the antigen corresponding to the target antibody. If this specific antibody is present in the blood sample, it will bind to the antigen. In the subsequent reaction step, an enzyme-conjugated secondary antibody binds to the target antibody. Because of the enzyme, the substrate is transformed in a colour staining reaction. The antibody concentration in the test sample can be determined by comparing the colour reaction product with that of standards of known concentrations.

Having a high concentration of eosinophils (eosinophil granulocytes) in the blood.

Epidemiology is 'the study of the frequency, distribution, and determinants of disease in human populations' according to the University of Washington's Department of Epidemiology.
Epidemiological information is used to plan and evaluate strategies to prevent illness and as a guide to the management of patients in whom disease has already developed.



Fluorescence immunoassay







Indirect immunofluorescence 

Inflammatory bowel diseases (IBD)
Inflammatory bowel diseases are a group of chronic disorders of the gastrointestinal tract that may occur at various times over a lifetime. The main IBD entities are Crohn’s disease (CD) and ulcerative colitis (UC).







Likelihood ratio

The likelihood ratio incorporates both the sensitivity and specificity of the test and provides a direct estimate of how much a test result will change the odds of having a disease.



Malar rash
Malar rash is also called butterfly rash, and is a medical sign consisting of a characteristic form of facial rash. It is often seen in lupus erythematosus, but is not pathognomonic. It can also be seen in other diseases such as dermatomyositis, pellagra and Bloom syndrome.

Mixed connective tissue disease (MCTD)
MCTD, or overlap syndrome, is characterized by the overlapping symptoms of different connective tissue diseases (systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), scleroderma, polymyositis, dermatomyositis, Sjögren's syndrome (SS)). Typical findings are high titres of autoantibodies against ribonuclease P (U1-RNP). Anti-nuclear antibodies and rheumatoid factors are among others that can be also detected. Treatment of MCTD is similar to that of scleroderma or SLE.



Negative likelihood ratio
The likelihood ratio for a negative result (negative LR) tells you how much the odds of the disease decrease when a test is negative.





neg LR =








(TP = True positives, TN = True negatives, FP = False positives, FN = False negatives)

Nonsteroidal anti-inflammatory drugs





Disease-causing organism.

Positive likelihood ratio
The likelihood ratio for a positive result (positive LR) tells you how much the odds of the disease increase when a test is positive.





pos LR =







1 – Specificity

(TP = True positives, TN = True negatives, FP = False positives, FN = False negatives)

Positive predictive value (PPV)
The positive predictive value (PPV), or precision rate, or post-test probability of disease, is the proportion of patients with positive test results who have the disease. Predictive value is related to the sensitivity and specificity of the test or screening method.




Number of patients positive








Number of positive results

(TP = True positives, FP = False positives)

The number of cases of disease in a population at a given time (frequency).



all patients with disease

Prevalence rate





all patients tested


Primary biliary cirrhosis (PBC)
PBC is an autoimmune liver disease. It is caused by the destruction of the small bile ducts in the liver, which leads to the accumulation of bile followed by damage to the liver tissue.  

Primary response
Initial immune response (cellular or humoral) after the first exposure to a specific antigen.

Pre-test probability
The prevalence of disease in a specified group of subjects. While the overall prevalence may be known, for each individual the disease status may be unknown before a diagnostic test and is therefore called the pre-test probability.
Post-test probability
The probability of disease after a given test result. Its value depends on the pre-test probability of the disease and the test's sensitivity and specificity.





The ability of a test to obtain the same results under the same conditions.

Rheumatoid arthritis
Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease affecting synovial joints, predominantly of the hands, and leads ultimately to joint deformation. Symptoms include symmetric joint inflammation, particularly in the hands, morning stiffness in joint(s), pain, swelling, tenderness, fatigue, malaise, diffuse musculoskeletal pain, weight loss, flu-like symptoms and anaemia.



Scleroderma, or progressive systemic sclerosis (PSS), is characterized by fibrosis of the connective tissue with preferential involvement of the skin, vessels, lungs, pleura, myocardium, pericardium, oesophagus and small intestine. The cause of this multisystem disease is unknown.


Sensitivity is the number of true-positive test results.




Number of true positives

Sensitivity =







Number of patients with this disease

(TP = True positives, FN = False negatives)


Specificity is the number of negative results in persons who do not have the disease (true-negative results in controls).




Number of true negatives

Specificity =







Number of controls

(TN = True negatives, FP = False positives)



Thyroid diseases (autoimmune-related)
In autoimmune thyroid diseases, the thyroid gland is underactive, as in Hashimoto's thyroiditis, or overactive as in Graves' disease, due to the existence of autoantibodies against thyroglobulin (TG) and thyroid-stimulating hormone (TSH).
Symptoms of Hashimoto's thyroiditis include depression, mania, sensitivity to heat and cold, paraesthesia, fatigue, panic attacks, constipation, migraines, muscle weakness, cramps, memory loss, infertility and hair loss.
Symptoms indicating Graves' disease are goitre, hypertension, weakness, muscle weakness, muscle degeneration, increased appetite, weight loss, insomnia, tremor, shortness of breath, increased sweating, heat intolerance, warm and moist skin, thin and fine hair and brittle nails.





Vasculitis is an inflammation of a blood or lymph vessel. Vasculitis can be divided into large-vessel, medium-sized vessel, and small-vessel vasculitis. Each group contains different diseases. 



Wegener's granulomatosis
Granulomatous inflammation of the respiratory tract and necrotizing vasculitis of the small to medium-sized blood vessels.
Wegener's granulomatosis is in the group of systemic vasculitis diseases involving small vessels.