Anti – RNP Antibody Test

Anti-RNP Ab level is increased in 100 % of the patients who have MCTD. About 38 to 44 % of the patients have increased level of anti-RNP Ab in SLE (systemic lupus erythematosus). After the positive result of the antinuclear antibody (ANA) and high clinical evidence of SLE or MCTD, anti-RNP Ab test is performed. 

SLE, dermatomyositis or polymyositis, Reynaud phenomenon, systemic sclerosis, and anti-RNP Abs are present as the symptoms which are associated with the MCTD. It is unknown that MCTD is a separate disease a subgroup of SLE or a syndrome. In SLE if anti-RNP Abs are present, this leads to the reduced rated of Raynaud phenomenon and milder renal damage. 

There is not any condition in which this test may not be conducted. If the ANA test result is negative, then this test provides very minimal information. 

The normal range and abnormal range depend on the laboratory. It is necessary to consider specific guidelines which is established by the laboratory. ELISA is used to quantify the autoantibodies IgG class in the anti-RNP Ab test. 

As per one laboratory, there may be parameter which are mentioned below are acceptable: 

The normal range is 20 U to 25 U. The result is positive if the value is greater than 26 U. If the value is less than 20 U, the result is negative. 

When the level of anti-RNP antibody is negative, it is not considered for the diagnosis of MCTD . The connective tissue disease are linked to raised levels of anti-RNP antibody which is an important criteria for the diagnosis of MCTD. The connective tissue diseases are linked to raised levels of anti-RNP antibody which is an important criteria for the diagnosis of MCTD. It is also important in the MCTD diagnostic. In MCTD, the sensitivity is about 95 % to 100 %, and the titer value is high, about 1:100000. In other rheumatologic disease, the titer value is low. 

In different rheumatologic diseases, the sensitivity of anti-RNP Ab: 

Rheumatoid arthritis – 10 % 

Scleroderma and Discoid lupus erythematosus (DLE) – 20 % to 30 % 

Systemic lupus erythematosus (SLE) – 38 % to 44 % 

As per the study of Ordonez-Canizares et. al, anti-RNP Abs are linked to the poly autoimmunity in patients with SLE. The OR (odds ratio) is 5.095. 

Sample type: Serum 

Sample collection container: Red-top tube 

Unacceptable samples: Samples which are hemolyzed or lipemic samples 

Sample volume: 1 ml, minimum volume: 0.3 ml 

Samples storage: Samples can be stored for 5 days at 2 °C to 8 °C or 6 months at -20 °C. 

Considerations: The duration and severity of the disease is not determined by the titer value or degree of positivity of the anti-RNP Ab test. 

Panels: Extractable Nuclear Antigens (ENA) panel comprise of other tests such as Anti-La test, anti-RO test, and Anti-Sm test along with anti-RNP Ab test which is linked to the ANA test.