Many laboratory tests are based on immune principles, such as blood typing in the blood bank (described later). However, we also have lab tests for the immune function itself. Detecting autoimmune diseases is one such example. Some standard testing techniques when testing for anti-nuclear antibodies involved in diseases such as systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA) include:
- ELISA - enzyme linked immunosorbant assay. Patient serum is added to nuclear antigen-coated 96-well plates and allowed to incubate. An enzyme-labeled antibody is then allowed to detect any attached anti-self antibodies. Finally, the substrate for the enzyme is added, which allows a reaction (color change) to occur in proportion to the amount of antibody. The reaction color change is detected in a spectrophotometer.
- CLIA - chemiluminescence immunoassays. The principle is similar to the above, except the label emits a photon of light instead of color.
- FANA - fluorescent antinuclear antibody testing, also known as ANA. Patient serum is added to a glass slide coated with a monolayer of cells. Anti-self antibodies will attach to parts of the cells - for instance, DNA, histones, centromeres, nucleoli, etc. A fluorescently labeled anti-antibody is then added, allowing those specific parts of the cell to fluoresce. The slide is then examined using a fluorescence microscope. Different patterns of fluorescence correlate with other parts of the cell to which the patient had formed antibodies. The image to the right illustrates different patterns of fluorescence.
The first two techniques lend themselves to automation and thus are widely used. However, manufacturer results vary; fluorescent antinuclear antibody tests are the gold standard.
Many other autoimmune diseases besides those that form antinuclear antibodies can be tested for. Some examples include autoimmune thyroid diseases, anti-phospholipid antibodies, celiac disease, type I diabetes mellitus, and auto-immune liver disease. Laboratory tests are done for many of these; however, discussing these many tests is beyond this introductory concept course.
