Test Id : SM
Smith (Sm) Antibodies, IgG, Serum
Useful For
Suggests clinical disorders or settings where the test may be helpful
Evaluating patients with clinical features suggestive of antinuclear antibody associated connective tissue disease and the confirmation of a diagnosis of systemic lupus erythematosus.
Testing for Smith 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.
Method Name
A short description of the method used to perform the test
Multiplex Flow Immunoassay
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
Anti-Smith (Sm) Antigen
Autoantibodies to Sm (Smith)
Sm (Anti-Sm) (Smith)
Sm (Smith) Autoantibodies
Smith Antigen
SmRNP Autoantibodies
Smth
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
Specimen Type
Describes the specimen type validated for testing
Serum
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
Special Instructions
Library of PDFs including pertinent information and forms related to the test
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
0.35 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | OK |
| Heat treated | Reject |
Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 21 days | |
| Frozen | 21 days |
Useful For
Suggests clinical disorders or settings where the test may be helpful
Evaluating patients with clinical features suggestive of antinuclear antibody associated connective tissue disease and the confirmation of a diagnosis of systemic lupus erythematosus.
Testing for Smith 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.
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by circulating autoantibodies to many intracellular targets. Of these autoantibodies, the anti-Smith (Sm) antibody associated with a positivity for antinuclear antibodies (ANA) is one of the earliest to be described.(1) The Sm antigen is a complex molecule consisting of a group of core proteins with molecular weights ranging from 9 to 29.5 kDa [B (B1, 28 kDa), B’ (B2, 29 kDa), N (B3, 29.5 kDa), D1 (16 kDa), D2 (16.5 kDa), D3 (18 kDa), E (12 kDa), F (11 kDa), and G (9 kDa)].(2) Of these core proteins, the B and D polypeptides are frequently targeted by the Sm autoimmune response.(3) The Sm proteins, together with ribonucleoproteins and small nuclear RNA form a RNA-protein complex or small nuclear ribonucleoprotein, which is involved in precursor messenger RNA (mRNA) splicing, a process which ultimately leads to mature mRNA generation.(4)
The presence of antibodies to Sm is specific for SLE with a sensitivity of 5% to 30%.(1) Based on the 2019 American College of Rheumatology/European League Against Rheumatism classification criteria for SLE, patients positive for anti-Sm antibodies already fulfil 60% of the criteria required for SLE classification.(5,6) However, anti-Sm antibodies may occur together ribonucleoprotein antibodies in certain ANA-associated connective tissue disease such as mixed connective tissue disease, systemic sclerosis and idiopathic inflammatory myopathies.(7) In a recent study, patients double-positive for anti-dsDNA and anti-Sm antibodies at the time of the diagnosis of SLE were reported to be at higher risk of flares and may benefit from stringent monitoring and early preventive treatment.(8) In addition, some studies have suggested that positivity for anti-Sm antibody may be dependent on patient’s ethnicity.(8)
In routine clinical practice, antigen-specific (solid-phase) immunoassays such as enzyme-linked immunosorbent assays, addressable laser bead immunoassays, line immunoassays, chemiluminescent immunoassays, BioPlex immunoassay and fluorescent enzyme immunoassays are widely used in determination of anti-Sm antibodies.(6,9) These immunoassays use, either a mixture of (native) Sm antigens or a specific (recombinant) Sm antigen, usually obtained by purification of nuclear extract or produced by in vitro translation, respectively, coated to a solid phase (e.g. plate/well, membrane, bead).(6) In the past, anti-Sm tests used a mixture of all Sm proteins purified from a native source. These mixtures often also contained other proteins, such as U1-RNP, which must be taken into consideration when interpreting results. Based on the analytical differences in immunoassays for detecting anti-Sm antibodies, the method used for their detection is likely to impact the diagnostic performance characteristics.
For more information see:
Connective Tissue Disease Cascade
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 anti-Smith antibody result in the appropriate clinical context is consistent with a diagnosis of systemic lupus erythematosus.
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1. Tan EM, Kunkel HG. Characteristics of a soluble nuclear antigen precipitating with sera of patients with systemic lupus erythematosus. J Immunol. 1966;96(3):464-471
2. Zieve GW, Khusial PR. The anti-Sm immune response in autoimmunity and cell biology. Autoimmun Rev. 2003;2(5):235-240
3. Billings PB, Hoch SO. Characterization of U small nuclear RNA-associated proteins. J Biol Chem. 1984;259(20):12850-12856
4. Battle DJ, Kasim M, Yong J, et al. The SMN complex: an assembly machine for RNPs. Cold Spring Harb Symp Quant Biol. 2006;71:313-320
5. Aringer M, Costenbader K, Daikh D, et al. 2019 European League Against Rheumatism/American College of Rheumatology Classification Criteria for Systemic Lupus Erythematosus. Arthritis Rheumatol. 2019;71(9):1400-1412
6. van Beers JJBC, Schreurs MWJ. Anti-Sm antibodies in the classification criteria of systemic lupus erythematosus. J Transl Autoimmun. 2022;5:100155
7. Migliorini P, Baldini C, Rocchi V, Bombardieri S. Anti-Sm and anti-RNP antibodies. Autoimmunity. 2005;38(1):47-54
8. Kwon OC, Park MC. Risk of systemic lupus erythematosus flares according to autoantibody positivity at the time of diagnosis. Sci Rep. 2023;13(1):3068
9. Llorente MJ, Jimenez J, Gonzalez C, et al. Effectiveness of different methods for anti-Sm antibody identification. A multicentre study. Clin Chem Lab Med. 2005;43(7):748-752
Method Description
Describes how the test is performed and provides a method-specific reference
Affinity-purified Sm antigens are bound to polystyrene microspheres, which are impregnated with fluorescent dyes to create a unique fluorescent signature. Sm antibodies, if present in diluted serum, bind to the Sm antigens on the microspheres. The microspheres are washed to remove extraneous serum proteins. Phycoerythrin (PE)-conjugated antihuman IgG antibody is then added to detect IgG anti-Sm bound to the microspheres. The microspheres are washed to remove unbound conjugate, and bound conjugate is detected by laser photometry. A primary laser reveals the fluorescent signature of each microsphere to distinguish it from microspheres that are labeled with other antigens, and a secondary laser reveals the level of PE fluorescence associated with each microsphere. Results are calculated by comparing the median fluorescence response for Sm microspheres to a 4-point calibration curve.(Package insert: Bioplex 2200 ANA Screen. Bio-Rad Laboratories; 02/2019)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.
Monday through Saturday
Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.
Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location
Indicates the location of the laboratory that performs the test
Fees :
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.
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Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.
This test has been cleared, approved, or is exempt by the US 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
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
CPT codes are provided by the performing laboratory.
CPT codes are provided by the performing laboratory.
86235
LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| SM | Sm Ab, IgG, S | 18323-6 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| SM | Sm Ab, IgG, S | 18323-6 |