Test ID SM Sm Antibodies, IgG, Serum
Specimen Required
Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Specimen Volume: 0.5 mL
Useful For
Evaluating patients with signs and symptoms of a connective tissue disease in whom the test for antinuclear antibodies is positive
Testing for Sm antibodies is not useful in patients without demonstrable antinuclear antibodies.
Testing Algorithm
See Connective Tissue Disease Cascade (CTDC) in Special Instructions.
Special Instructions
Method Name
Multiplex Flow Immunoassay
Reporting Name
Sm Ab, IgG, SSpecimen Type
SerumSpecimen Minimum Volume
0.35 mL
Specimen Stability Information
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Serum | Refrigerated (preferred) | 21 days | |
Frozen | 21 days |
Clinical Information
Sm (Smith) is a small nuclear ribonucleoprotein composed of several protein autoantigens designated B, B1, D, E, F, and G, which range in size from 11 kD to 26 kD. Sm antibodies are specific for lupus erythematosus (LE) and occur in approximately 30% of LE patients. The levels of Sm antibodies remain relatively constant over time in patients with LE and are usually found in patients that also have RNP (ribonucleoprotein) antibodies.(1,2)
Sm is 1 of 4 autoantigens commonly referred to as extractable nuclear antigens (ENA). The other ENA are RNP, SS-A/Ro, and SS-B/La. Each ENA is composed of 1 or more proteins associated with small nuclear RNA species (snRNA) ranging in size from 80 to approximately 350 nucleotides. Antibodies to ENA are common in patients with connective tissue diseases (systemic rheumatic diseases) including LE, mixed connective tissue disease, Sjogren syndrome, scleroderma (systemic sclerosis), and polymyositis/dermatomyositis.
See Connective Tissue Disease Cascade (CTDC) in Special Instructions.
Reference Values
<1.0 U (negative)
≥1.0 U (positive)
Reference values apply to all ages.
Interpretation
A positive result for anti-Sm antibodies is consistent with a diagnosis of lupus erythematosus.
Clinical Reference
1. Homburger H, Larsen S: Detection of specific antibodies. In Clinical Immunology: Principles and Practice. First edition. Edited by R Rich, T Fleisher, B Schwartz, et al. St. Louis, Mosby-Year Book, 1996, pp 2096-2109
2. Kotzin B, West S: Systemic lupus erythematosus. In Clinical Immunology Principles and Practice. Second edition. Edited by R Rich, T Fleisher, W Shearer, et al. St. Louis, Mosby-Year Book, 2001, pp 60.1-60.24
Day(s) and Time(s) Performed
Monday through Saturday; 4 p.m.
Analytic Time
1 dayTest Classification
This test has been cleared, approved or is exempt by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.CPT Code Information
86235
LOINC Code Information
Test ID | Test Order Name | Order LOINC Value |
---|---|---|
SM | Sm Ab, IgG, S | 18323-6 |
Result ID | Test Result Name | Result LOINC Value |
---|---|---|
SM | Sm Ab, IgG, S | 18323-6 |