Rheumatoid factor
(RF)

is the autoantibody that was first found in rheumatoid arthritis. It is defined as an antibody against the Fc portion of IgG and different RFs can recognize different parts of the IgG-Fc. RF and IgG join to form immune complexes that contribute to the disease process

sample type:

Serum separator tube or plasma separator tube. Also acceptable: Green (lithium heparin), lavender or pink

Uses:

Rheumatoid factor blood test helps to diagnose rheumatoid arthritis. Rheumatoid factor is an antibody that is detectable in the blood of approximately 80% of adults with rheumatoid arthritis. Rheumatoid factor test is used by health care professionals to help in diagnosing rheumatoid arthritis.

Precaution:

The RF test doesn’t require any food, drink, or medication restrictions, nor do the other tests you may have with it. If you have different blood tests than those mentioned here, you may need to fast before the test. Your healthcare provider will give you specific instructions

Interfering factors:

Interference by Rheumatoid Factor in Immunoglobulin M-Class Herpes Simplex Virus Types 1 + 2 Immunoassays

Herpes simplex virus (HSV) types 1 + 2 immunoglobulin (Ig)M antibodies assays are important tools for diagnosing pregnant women and their newborns. However, it is unclear whether high levels of rheumatoid factor (RF) interfere with serological methods used to test for HSV types 1 + 2 type-specific IgM antibodies. We report a case of a false-positive result for HSV 1 + 2 IgM antibodies due to gross overestimation of RF by enzyme-linked immunosorbent assay (ELISA)

Pre analytical errors:

Bacterial contamination of controls and specimens as well as freezing and thawing of the RF-Latex Reagent may lead to false positive results. Traces of detergent in the test cards may give false positive results.

corrective action:

Studies of the diagnostic utility of rheumatoid factor (RF) testing for rheumatoid arthritis (RA) conducted in early arthritis clinics in secondary care have reported sensitivity and specificity of 69% and 85% respectively

Post analytical errors:

1- failure to report test results,

2-delay in reporting,

3-incorrect calculation,

4-critical results not reported or delayed,

5- and results sent to the wrong patient.

Reference rang:

the “normal” range (or negative test result) for rheumatoid factor is less than 14 IU/ml.

Any result with values 14 IU/ml or above is considered abnormally high, elevated, or positive