TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
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Test ID: SM    
Sm Antibodies, IgG, Serum

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Useful For Suggests clinical disorders or settings where the test may be helpful

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 Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

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

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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 Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

<1.0 U (negative)

> or =1.0 U (positive)

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

A positive result for anti-Sm antibodies is consistent with a diagnosis of lupus erythematosus.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements.

Clinical Reference Recommendations for in-depth reading of a clinical nature

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

Special Instructions Library of PDFs including pertinent information and forms related to the test