Assay

Extractable Nuclear Antigen (ENA) antibodies

Key Words

Extractable Nuclear Antigen antibodies, ENA

Specimen Collection

Serum (Brown)

Turnaround time

10 days

Test indications

If the ANA screen is positive than an ENA screen will be performed which contains antigens to the following ENA antibodies (Ro, La, Sm, U1RNO, Jo-1, Scl-70) and centromere. If the ENA screen is equivocal or positive then an ENA profile will be undertaken to screen for the individual autoantibodies contained in the screen.

ENA is a term used to describe antibodies to the soluble components of the nuclear. At the moment six main antibodies are recognised;

Sm: specific for SLE but found in only 20-30% of SLE patients with a higher incidence in non-Caucasians, especially those of Afro-Caribbean descent. There is no correlation with disease activity.

U1RNP: A high titre positive result of only U1RNP is diagnostic for MCTD but these antibodies are also found in 30-40% of SLE patients.

Ro or SS-A: The Ro (SS-A) antigen also occurs in the cell cytoplasm and very rarely a serum may be positive for Ro antibodies even in the absence of an ANA. These antibodies can cause congenital heart block and is recommended that all female patients suspected SLE or Sjögren’s syndrome are screened for anti SS-A (Ro) antibodies especially is they are considering pregnancy. These antibodies are associated with Sjögren’s syndrome (up to 75% in primary Sjögren’s), Sicca syndrome, and in many cases of Sjögren’s syndrome secondary to a variety of other autoimmune diseases. They are also found in variants of SLE including subacute cutaneous lupus and neonatal lupus with congenital heart block and also in SLE resulting from homozygous C2 and C4 deficiency.

La or SS-B: Usually found with anti-Ro in both primary and secondary Sjögren’s syndrome and SLE. Sjögren’s patients with anti-La are likely to have more extra glandular disease.

Jo-1: Antibodies to aminoacyl-tRNA histidyl synthetase. These are associated with inflammatory muscle disease, especially idiopathic polymyositis.

Scl-70: (Antibodies to Topoisomerase-I an enzyme catalysing and breaking and re-joining of ssDNA). These are found in 20-40% of patients with systemic sclerosis, it is associated with facial skin, kidney and heart involvement, ischaemic fingertip ulcers and pulmonary fibrosis.

Methodology

Enzyme Immunoassay

Interferences

No known methodological interferences

Reference Range

N/A

Analytical error

Contact laboratory (x8454)

Reference change value

N/A

Minimum retesting interval

Requests for ENA investigations within one year of a previous request are intervened.