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Anti SM, Anti-Smith, ENA
MessagePerformed in the Chemistry Laboratory, Tufts Medical Center X5820
Test Code
SM
CPT Codes
86235
Preferred Specimen
Serum, Gold top
Acceptable: Red top
Minimum Volume
0.5 mL
Transport Container
Gold Top (SST)
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 8 hours
Refrigerated: 5 days
Frozen: One year
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Grossly lipemic, hemolyzed, or microbially specimens should not be used.
Methodology
Quantitative indirect immunofluorescence on the Phadia 250 (ThermoFisher Corp.)
Setup Schedule
This assay is performed twice per week.
Reference Range
<7.0 IU/mL (negative)
7.0-10.0 IU/mL (equivocal)
>10.0 IU/mL (positive)
Negative is considered normal. Reference values apply to all ages.
7.0-10.0 IU/mL (equivocal)
>10.0 IU/mL (positive)
Negative is considered normal. Reference values apply to all ages.
Clinical Significance
The determination of antinuclear antibodies (ANA) is of central importance for the clinical diagnosis of connective tissue diseases. Anti-Sm antibodies react with the protein subunits BB’ and D. However, tests which include BB’ fail to differentiate patients with SLE from those with other autoimmune diseases. This test uses only a peptide from the D subunit, rendering it more specific. Sm antibodies, and particularly those against the SmD component, are specific but comparatively insensitive as clinical marker for SLE. Indeed, their prevalence ranges from 20 % to 30 % in SLE.
