Extractable Nuclear Antibodies (ENA) Blood Test

The ENA (Extractable Nuclear Antigen) screen is a comprehensive test that detects the presence of any extractable nuclear antibodies in the blood. This screening test identifies whether autoantibodies are present before specific antibody types are identified. A positive ENA screen indicates the presence of one or more of the specific ENA antibodies, prompting further investigation to determine which specific antibodies are present and their clinical significance.

Anti-ribonucleoprotein (anti-nRNP) antibodies target U1 small nuclear ribonucleoprotein. These antibodies are found in various connective tissue diseases, including systemic lupus erythematosus (SLE), systemic sclerosis, and polymyositis. High levels of anti-RNP antibodies are the defining feature of mixed connective tissue disease (MCTD), a condition that shares features of multiple autoimmune disorders. The presence of these antibodies is associated with Raynaud's phenomenon, arthritis, and muscle inflammation.

Anti-Smith (anti-Sm) antibodies target Smith proteins, which are components of small nuclear ribonucleoproteins. These antibodies are highly specific for systemic lupus erythematosus (SLE), though they are only present in about 20–30% of SLE patients. The presence of anti-Sm antibodies is one of the diagnostic criteria for SLE and is associated with more severe disease manifestations, including kidney involvement and central nervous system complications.

Anti-Ro antibodies, also called anti-SS-A antibodies, target Ro/SS-A proteins. These antibodies are found in approximately 40–60% of people with Sjögren's syndrome and 30–40% of those with systemic lupus erythematosus (SLE). Anti-Ro antibodies can cross the placenta during pregnancy and are associated with neonatal lupus and congenital heart block in babies born to mothers with these antibodies. Results outside the normal range may need a follow-up with your GP.

Anti-La antibodies, also known as anti-SS-B antibodies, target the La/SS-B protein. These antibodies are commonly found in Sjögren's syndrome, often appearing alongside anti-Ro antibodies. Anti-La antibodies are also associated with systemic lupus erythematosus (SLE) and neonatal lupus. Their presence in pregnant women with SLE is linked to a lower risk of congenital heart block in the baby compared to anti-Ro antibodies alone.

Anti-Jo-1 antibodies target histidyl-tRNA synthetase, an enzyme involved in protein synthesis. These antibodies are the most common type of anti-synthetase antibodies and are strongly associated with polymyositis and dermatomyositis. Patients with anti-Jo-1 antibodies often develop antisynthetase syndrome, characterised by muscle inflammation, interstitial lung disease, arthritis, Raynaud's phenomenon, and mechanic's hands (rough, cracked skin on the fingers).

Anti-Scl 70 antibodies, also known as anti-topoisomerase I antibodies, target the DNA topoisomerase I enzyme. These antibodies are highly specific for systemic sclerosis (scleroderma), particularly the diffuse cutaneous form. Their presence is associated with more severe disease, including widespread skin thickening, interstitial lung disease, and pulmonary fibrosis. Anti-Scl 70 antibodies are found in approximately 20–30% of people with systemic sclerosis.

Anti-centromere protein B (anti-CENP-B) antibodies target proteins in the centromere region of chromosomes. These antibodies are highly specific for limited cutaneous systemic sclerosis (lcSSc), also known as CREST syndrome. Their presence is associated with Raynaud's phenomenon, skin thickening limited to hands and face, and a generally better prognosis compared to diffuse scleroderma. Results outside the normal range may need a follow-up with your GP.