RF

Rheumatoid Factor (RF)

The diagnosis of Rheumatoid arthritis is based on clinical assay, but the laboratory and radiological tests are useful to confirm clinical diagnosis and to evaluate the seriousness and the phase of the disease. Rheumatoid Factor (RF) in serum is one of the main clinical markers for rheumatoid arthritis. RF is a term used to describe a group of antibodies (IgM, IgG and IgE) directed towards the antigenic site on the Fc portion fragment of the human and animal body's own IgG antibodies. 

Rheumatoid Factor Testing: clinical testing supplies designed to identify the presence of Rheumatoid Factor (RF) in patient blood samples and aid in diagnosing rheumatoid arthritis. RF-latex serology kit test is an indirect agglutination kit for the detection of Rheumatoid Factor (RF) in human serum using latex particles coated with human IgG. 

PRINCIPLE: RF-Latex Test is a rapid agglutination procedure, developed for the direct detection and the semi-quantitation on a slide of rheumatoid factors (RF) in serum. Imuno Latex RF is a very sensitive test and is performed by testing a suspension of polystyrene latex particles coated with purified and stabilized human gamma globulin IgG and suspended in glycine buffer pH 8.2, against unknown serums. The reagent is based on an immunological reaction between human IgG bound to biologically inert latex particles and rheumatoid factors in the test specimen. The presence or absence of a visible agglutination indicates the presence or absence of RF in the samples tested. 

When serum containing rheumatoid factors is mixed with the latex reagent, visible agglutination occurs. The suspension of latex is mixed on a test card with serum containing elevated rheumatoid factor levels; a clear agglutination is seen in 2 minutes. 

The RF latex reagent sensitivity has been adjusted to detect a minimum of 8 IU/mL of rheumatoid factors according with the WHO International Standard without previous sample dilution. The regular kit contains: suspension of latex, positive control serum, negative control serum, stirrers, test card, instructions for use.

REAGENT COMPOSITION - RF-Latex Reagent: Suspension of polystyrene latex particles coated with human gamma globulin in a buffered saline solution. CONTROL + Human serum with an activity equivalent to appr. 25 IU/mL. CONTROL - Animal serum with an activity < 5 IU/mL. Precautions: Components of different human origin have been tested and found to be negative for the presence of antibodies anti-HIV 1+2 and anti-HCV, as well as for HBsAg.

EXPECTED VALUES: Of those patients with a clinical diagnosis of rheumatoid arthritis approximately 70-80% are seropositive for rheumatoid factor. Positive results were shown for nearly all patients with variants of rheumatoid arthritis. A positive result can be expected in less than 5% of healthy individuals, while in the population aged 60 years and older as many as 30% may be seropositive using latex tests for the detection of rheumatoid factor. 

CLINICAL SIGNIFICANCE: Rheumatoid factors are found in the sera of most patients with rheumatoid arthritis as well as in a variety of other diseases. Rheumatoid factors testing has a high diagnostic value on a tentative diagnosis made on the basis of case history and clinical findings. 

ANALYTICAL PERFORMANCE: The minimum detectable unit (analytical sensitivity) is of approximately 8 IU/mL (6-16 IU/mL).  

LIMITATIONS OF THE PROCEDURE: Positive reactions do occur in conditions other than rheumatoid arthritis such as mononucleosis, hepatitis C, syphilis, various other infections and in elderly patients. When tested by the quantitative test, however, most of these specimens give very low results.