What is an anti-ENA screen?

This test is used to help diagnose, distinguish and monitor the progression of different autoimmune diseases. Connective tissue is found throughout the human body. It is made up of cells and rigid fibres such as collagen and elastic fibres, among others, and its role is to envelop, separate and protect other body tissues. Connective tissue envelops large organs such as the liver or kidneys, strengthens joints, tendons and ligaments, and supports small blood vessels such as arterioles. The skin is particularly rich in connective tissue. Collagen (or connective tissue) disease refers to a group of disorders affecting these collagen-rich tissues.

The immune system is responsible for defending the body against attacks from foreign cells and organisms: bacteria, viruses, parasites and transplanted cells. Often, the immune system goes awry and confuses some of its own tissues as foreign. The production of antibodies against its own tissues is the cause of a large number of “autoimmune” diseases. In addition to the collagen disorders mentioned above, pernicious anemia, juvenile diabetes and some thyroid disorders are autoimmune in origin. Depending on the cellular substances involved, different types of collagen diseases can be diagnosed, including rheumatoid arthritis, systemic lupus erythematosus (SLE), Sjögren’s (or sicca) syndrome, scleroderma, polymyositis and mixed connective tissue disease.

The abbreviation “ENA” stands for “extractable nuclear antigens.” Therefore, anti-ENA antibodies are directed against components that can be extracted from the cell nuclei of collagen-rich tissue.

An anti-ENA screen determines the levels of seven different autoantibodies including anti-Sm, anti-RNP, anti-SSA, anti-SSB, anti-Jo-1, anti-Scl 70 and anti-CENP-B. Each antibody (or combination of antibodies) is specific to a different collagen disease.

An anti-ENA screen is usually prescribed following a positive result in an antinuclear antibody (ANA) test. While the ANA test suggests the presence of an autoimmune disorder, an anti-ENA panel makes it possible to distinguish between many different collagen diseases.

Suggestive symptoms of collagen disease are varied and may include the following:

• Persistent fever and fatigue
• Muscular aches and pains
• Pain or swelling in certain joints
• Skin rashes
• Sensitivity to ultraviolet light (after sun exposure)
• Raynaud syndrome (fingers turn white in response to cold) * Proteinuria (proteins in the urine)
• Neurological symptoms such as convulsions, depression or psychosis
• Lowered red blood cell count (hemolytic anemia) or white blood cell count (leucopenia)

The diagnosis of different collagen diseases is based on a combination of clinical observations (signs and symptoms) and positive autoantibody tests. In general, when antibodies are positive in an individual showing appropriate signs and symptoms, a diagnosis of collagen disease is highly likely.

When antibodies are negative in an individual with typical signs and symptoms of a collagen disease, it could mean that the production of antibodies is still too low or that the signs and symptoms are due to another disease.

A positive result in a symptomatic patient is based on the following test combinations

Anti-RNP: Positive in more than 95% of individuals with mixed connective tissue disease. May also be positive in systemic lupus erythematosus (SLE) and scleroderma.

Anti-Sm: Positive in about 30% of individuals with SLE. However, their presence is very specific to this disease.

Anti-SSA: Positive in 75% of patients with Sjögren’s syndrome; may also be positive in SLE and scleroderma.

Anti-SSB: Positive in 60% of patients with Sjögren’s syndrome; may also be positive in SLE and scleroderma. Usually accompanied by a positive anti-SSA result.

Anti-Scl 70: Positive in 60% of individuals with scleroderma. Very specific marker for this disease.

Anti-Jo-1: Positive in 30% of individuals with polymyositis; may also be positive in pulmonary fibrosis