| • | ENA = extractable nuclear antigens (four antibodies directed against small ribonucleoproteins (sRNP) consist of several molecules that contain RNA and an associated protein) |
| • | interpretation is technique specific: |
| • | radial immunodiffusion – lower sensitivity, higher specificity; therefore a positive test has a high diagnostic value |
| • | ELISA – highly sensitive, less specific; but able to quantify, therefore a high diagnostic value only when high levels of antibody are present |
U1RNP
| • | by definition, present in 100% of MCTD to the exclusion of other types of antinuclear antibodies |
| • | present in 30% SLE (but they have other ANA’s) |
| • | because the incidence of SLE is much higher than that of MCTD, the majority of patients with U1RNP antibodies have SLE rather than MCTD |
| • | patients may have an overlap syndromes without this antibody, but such patients do not have MCTD by definition (their condition is better described by the more general term “overlap CTD”) |
ANTI-SSA/RO
| • | mothers of infants with neonatal LE – 95% |
| • | children born to mothers with this antibody have an increased incidence of congenital heart block |
ANTI-SSB/LA
| • | if present, usually accompany Ro |
Sm ANTIBODIES
| • | highly specific for SLE (diagnostic by immunodiffusion) |
| • | should not be confused with anti-smooth muscle antibodies detected in autoimmune liver disease (sclerosing cholangitis) |
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