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 common 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 anti-antibody is then allowed to detect any anti-self antibodies that have attached. 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 different parts of the cell to which the patient had formed antibodies. The image to the right illustrates different patterns of fluorescence that can be seen.
The first two techniques lend themselves to automation and thus are widely used. However, results vary among manufacturers, and the gold standard is the fluorescent antinuclear antibody tests.
Many other autoimmune diseases can be tested for other than those which form antinuclear antibodies. Some examples include autoimmune thyroid diseases, anti-phospholipid antibodies, celiac disease, type I Diabetes Mellitus, auto-immune liver disease, and many others. Laboratory tests are done for many of these, however, discussion of these many tests is beyond this basic concept course.
