Sm and Sm/RNP Antibodies Test
This test measures antibodies to Sm and to RNP (ribonucleoprotein, also called anti-U1) together in one blood sample. Quest associates Sm antibody with systemic lupus erythematosus (SLE) and RNP antibody with SLE as well as Sjögren's syndrome, scleroderma and polymyositis.
About this test
Sm antibody is considered a marker for SLE, though Quest notes it is present in only about 20% of people with SLE. RNP antibody occurs more often, in about 45% of people with SLE, and is also seen in Sjögren's syndrome, scleroderma and polymyositis; elevated RNP levels specifically are associated with mixed connective tissue disease.
Quest also notes that in SLE, RNP antibodies have been associated with a relatively benign disease course, with lower rates of kidney and central nervous system involvement, and that RNP antibody positivity may be considered when RNP results are notably higher than Sm results.
Test details
| Quest code | 7448 |
|---|---|
| Methodology | Immunoassay |
| Sample type | 1 mL serum |
| Collection | Quest patient service center |
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Quest resources
Additional details
What this test looks at
The test reports two separate results: Sm antibody and Sm/RNP antibody levels, both from the same serum sample. Quest lists this product under several names, including Anti-Ribonucleic Protein Antigen, Anti-ENA Antibody, ENA Antibodies, Ribonuclear Protein Antibody, Anti-Smith Antibody and RNP Antibody, all referring to this combined measurement.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does this test measure?
It measures antibodies to Sm and to RNP (ribonucleoprotein, also called anti-U1) in a serum sample, using immunoassay methodology.
How is the sample collected?
The test uses a 1 mL serum sample from a routine blood draw.
Do I need to prepare for this test?
No preparation instructions are listed for this test, though people follow any instructions their ordering clinician provides.
What is the difference between Sm and RNP antibodies?
Quest reports Sm antibody in about 20% of people with SLE, while RNP antibody appears in about 45% of people with SLE and is also seen in Sjögren's syndrome, scleroderma and polymyositis; elevated RNP specifically relates to mixed connective tissue disease.
Can this test diagnose lupus on its own?
No. Quest describes these antibodies as markers considered alongside symptoms, history and other results; a clinician interprets the combined result in that context.
How much does the Sm and Sm/RNP Antibodies test cost?
The cash price at Celio Health is $215. That covers the physician's order and sample collection at a Quest patient service center — no insurance is needed and there's no separate doctor's visit to pay for.