Rheumatoid factor
is a test that measures the presence and level of rheumatoid factor (RF) in the blood.
The RF test is used mainly in the diagnosis of rheumatoid arthritis, although it can also be positive in many other diseases or healthy people.
The RF is an IgM antibody that recognizes immunoglobulin G ( IgG) as an antigen. Antibodies reacting against antigens form immune complexes. These immune complexes can activate the complement system and other inflammatory processes.
About 80% of patients with rheumatoid arthritis have positive RF tests, that is, titers > 1:80 (this means that the sample can be diluted 80 times while still being able to measure the presence of the IgM antibody).
| ESR | |
| A nonspecific screening test for various diseases. The test measures the distance (in millimeters) that red blood cells settle in unclotted blood toward the bottom of a specially marked test tube in 1 hour. | |
| Why the test is performed: | |
| The erythrocyte sedimentation rate (ESR) can be used to monitor inflammatory or malignant disease, rheumatic fever, and acute myocardial infarction. Although it is a screening test (not considered diagnostic for any particular disorder), it is useful in detecting and monitoring tuberculosis, tissue necrosis (tissue death), rheumatologic disorders, or an otherwise unsuspected disease in which symptoms are vague or physical findings are minimal. | |
| The hematocrit Definition: | |
| The hematocrit is the percent of whole blood that is comprised of red blood cells. The hematocrit is a compound measure of RBC number and size.
The HCT is almost always ordered as part of the complete blood count ( CBC). The CBC measures the number of red blood cells (RBCs), white blood cells (WBCs), the total amount of hemoglobin in the blood, and the fraction of the blood composed of cells (hematocrit). |
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| Alternative Names: HCT |
Rheumatoid Factor
Principle
- rheumatoid factor is an IgM antibody which binds to the Fc region of an IgG molecule
- such immune complexes may have a role in joint disease
Indication
- RF is found in the serum and synovial fluid of animals with immune-mediated arthritis, particularly rheumatoid arthritis.
Method
The Rose Waaler Assay
- detects RF by agglutination of IgG coated (sensitised) sheep erythrocytes
- control (unsensitised) RBC (no IgG) will not agglutinate
Results
- test serum (or synovial fluid) is serially diluted, so RF titre (last dilution causing agglutination of the sensitised RBC) is recorded.
Interpretation
- positive RF helps support a diagnosis of immune-mediated polyarthritis
- not all animals with rheumatoid arthritis will have RF
- low titred RF may be found in animals with chronic inflammatory or neoplastic disease (non-specific autoantibody)
The Antinuclear Antibody Test
Principle
- to determine whether serum from a patient contains circulating antibody specific for components of cell nuclei (e.g. DNA, RNA).
Indication
- animals suspected of having autoimmune disease, particularly multisystems autoimmunity
(systemic lupus erythematosus, SLE)
Method
| -binding is visualised by use of a secondary antibody linked to enzyme | |
| -serial dilutions of patient sera are incubated with a nucleated cell monolayer |
Results
- are reported as the ANA titre (reciprocal of last positive serum dilution)
Interpretation
- positive serum ANA is one of the diagnostic criteria for SLE
- high titred ANA supports a diagnosis of autoimmunity where there are appropriate clinicopathological signs
- low titred ANA may occur with a chronic inflammatory or neoplastic disease (ie. non-specific autoantibody)
Question
Examine the two ANA slides. Click on each well to see a magnified view.
A