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The RFscan™ Latex Test is intended for the qualitative or quantitative determination of circulating rheumatoid factors.

Rheumatoid factors are antibodies of various immunoglobulin classes which are directed against specificities in the Fc portion of IgG molecules. Serum rheumatoid factor (RF) appears most commonly, and in the highest titer, in patients with the chronic systemic disease rheumatoid arthritis.¹ These autoantibodies are detected in approximately 70% of adult rheumatoid arthritis patients.² Therapeutic measures can suppress the inflammatory manifestations of the disorder and aid in minimizing musculoskeletal dysfunction. Hence, serological tests for the early detection of RF have significant clinical applications.

Many disease states other than rheumatoid arthritis have been shown on occasions to give seropositive RF results. Some RF assays have returned positive results in patients with disseminated sarcoidosis, syphilis, essential hypertension and hepatitis.^1,3 Furthermore, a small number of healthy people, especially the elderly, may also have RF.⁴ As a rule these individuals display very low titers of RF and can usually be distinguished from rheumatoid arthritis patients by this means.

Using sheep erythrocytes sensitized with rabbit gamma-globulin, Waaler in 1940⁵ and Rose et al. in 1948⁶ related hemagglutination by human serum to the disease rheumatoid arthritis. In 1956, Singer and Plotz⁷ eliminated many of the variables associated with sheep erythrocytes by replacing the erythrocytes with biologically inert latex particles coated with gamma-globulin. This method serves as the basis for the RFscan Latex Test. Refinements in the preparation and stabilization of sensitized particles have led to an improved sensitivity and specificity of the test.

A positive and negative control are provided in each RFscan kit. The positive control should show agglutination, while the negative control should show no agglutination. If the Card Titration Method is used, the positive control should exhibit agglutination through the titer given in the Assay Value Information.

Precautions: in vitro Diagnostic

Reagents: Do not use beyond the expiration date. Upon removal from refrigeration, allow reagents to warm to room temperature (15 to 30°C) before use. Do NOT mix reagents from different kit lot numbers.

The RFscan Latex Antigen may require vigorous shaking to thoroughly resuspend. Keep the vial tightly closed when not in use to prevent evaporation of the suspension medium. The suspension should be milky and homogeneous. Do not use the reagent if it shows signs of flocculation.

To assure proper drop delivery hold dispensing bottles vertically, dispensing one free-falling drop at a time.

Controls: Do not use the kit if positive and negative controls do not yield appropriate results.

The serum controls are derived from human blood tested by an FDA (U.S. Food and Drug Administration)-approved method for the presence of the antibody to HIV (human immunodeficiency virus) and HBsAg (hepatitis B surface antigen) and found to be nonreactive.

Test Cards: Cards must be flat for proper reactions. If necessary, flatten cards by bowing back in a direction opposite to that of the curl. Care should be taken not to finger-mark the test areas, since this may result in an oily deposit and improper test results. Use each card once and discard. Store cards in the original package in a dry area at room temperature.

Reading of Test Results: Results should be read promptly under a high intensity incandescent lamp. Fluorescent lighting is generally insufficient to distinguish minimally reactive results. The use of magnification in reading test results is not recommended.