SM & RNP Antibodies

Test Code

Alias/See Also
Anti-ENA; Anti-RNP: Anti-Smith ABS; Anti-Smith Antibody; ENA; ENA Antibodies; ENA Screen; RNP Antibody; SM & RNP Antibodies; Smith Abs; 

CPT Codes

Preferred Specimen
1 mL serum (minimum 0.5 mL) 

SST or Red top: Avoid hemolysis. Invert a minimum of 5 times, then allow to clot in an upright position for 30 minutes. Centrifuge the the tube for at least 10 minutes. Keep tightly stoppered.

Transport Container
SST (speckled top), Red top , Plastic Vial (transfer) tube

Transport Temperature
Refrigerated (preferred)
     For specimen integrity in the lock box click here

Specimen Stability
Room Temperature = n/a
Refrigerated = 5 days
Frozen = at least 7 days


Setup Schedule
Even days of the week (Monday - Friday only) 7:00 am

Report Available
3 days

Reference Range
  SEX AGE Report Normals
SM Antibody N/M/F 1000Y < 20 = Negative
      > = 20 = Positive
  Values between 20 and 40 are weak positives and repeat testing is recommended in 3 - 6 months.   
  The presence of SM Antibodies is highly specific but relatively insensitive for SLE.  SM Antibodies reactivity is not definitively described in other diseases, although a few studies describe them in Monoclonal Gammopathy, Schizophrenia and Uveitis. 
RNP Antibody N/M/F 1000Y < 20 = Negative
      > = 20 = Positive
  Values between 20 and 40 are weak positives and repeat testing is recommended in 3 - 6 months. 
  RNP antibodies are found in Mixed Connective Tissue Disease (MCTD), SLE, RA, Sjogren's Syndrome, Progressive Systemic Sclerosis, and drug induced LE.  The presense of RNP Antibodies and the absence of SM and DS DNA Antibodies strongly suggest MCTD, while the absence of RNP usually rules out MCTD. 

Clinical Significance
Antibodies to Sm are highly specific for systemic lupus erythematosus (SLE) and when present are considered a marker antibody. However, these antibodies are found in only 20% of patients with SLE. RNP antibodies (also known as anti-u1 or ribonucleoprotein antibodies) are found in 45% of SLE patients but are also observed in numerous other disease states such as Sjögren's syndrome, scleroderma and polymyositis. Elevated levels of antibodies to RNP are seen in mixed connective tissue disease. In SLE, RNP antibodies have been associated with a relatively benign disease course with lower incidence of renal and central nervous system involvement. Patients may be considered positive for RNP antibodies when the RNP antibody result is significantly higher than the SM antibody result.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.