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Test ID SM Sm Antibodies, IgG, Serum

Useful For

Evaluating patients with signs and symptoms of a connective tissue disease in whom the test for antinuclear antibodies is positive

Testing Algorithm

See Connective Tissue Disease Cascade (CTDC) in Special Instructions.

Method Name

Multiplex Flow Immunoassay

Reporting Name

Sm Ab, IgG, S

Specimen Type

Serum

Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL

Specimen Minimum Volume

0.35 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 21 days
  Frozen  21 days

Clinical Information

Sm 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 antibodies.(1,2)

 

Sm is 1 of 4 autoantigens commonly referred to as extractable nuclear antigens (ENAs). The other ENAs are RNP, SS-A/Ro, and SS-B/La. Each ENA is composed of 1 or more proteins associated with small nuclear RNA species (snRNP) ranging in size from 80 to approximately 350 nucleotides. Antibodies to ENAs are common in patients with connective tissue diseases (systemic rheumatic diseases) including LE, mixed connective tissue disease, Sjogren's syndrome, scleroderma (systemic sclerosis), and polymyositis/dermatomyositis.

 

See Connective Tissue Disease Cascade (CTDC) in Special Instructions and Optimized Laboratory Testing for Connective Tissue Diseases in Primary Care: The Mayo Connective Tissue Diseases Cascade in Publications.

Reference Values

<1.0 U (negative)

≥1.0 U (positive)

Reference values apply to all ages.

Cautions

Testing for Sm antibodies is not useful in patients without demonstrable antinuclear antibodies.

Day(s) Performed

Monday through Saturday; 4 p.m., Sunday; 11a.m.

Report Available

1 day

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been cleared or approved 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

NY State Approved

Yes