Extractable Nuclear Antibodies (ENA) assay detects the presence of autoantibodies in the blood that react with proteins in the cell nucleus. It is used to confirm the presence of specific antibodies as follow-up after a positive ANA IFA test (specifically with speckled pattern). The ENAs are known as "extractable" because they can be removed from the cell nuclei using saline and represent six main proteins: SSA/Ro, SSB/La, Sm, RNP, Scl-70, and Jo-1.
SSA/SSB: Positive result supports the diagnosis of Sjogren's syndrome or other connective tissue diseases.
Sm: Positive result supports diagnosis of SLE with renal involvement
RNP: Positive result supports diagnosis of mixed connective tissue disease, which resembles SLE but is not accompanied by renal involvement.
Scl-70: Positive result supports diagnosis of scleroderma
Jo-1: Positive result supports diagnosis of polymyositis