Laboratory Testing for Extractable Nuclear Antigens

The ENA blood test is ordered when there are signs of an auto-immune disorder. Some of the auto-immune disorders which are screened for include mixed connective tissue disease, Sjögren’s syndrome, and lupus. The test is usually given after a positive result on the ANA blood test. The ANA, or antinuclear antibody test, screens for proteins that are present when the immune system fails to distinguish the body from foreign particles.

The symptoms which prompt a doctor to order an ENA blood test arise from the tissue and cellular damage caused by the immune system. Usually, the symptoms include inflammation of organs, muscle pain, joint pain, and fatigue.

The ENA blood test screens the blood for the presence of proteins that are produced when the immune system attacks its own body tissue. These proteins are called autoantibodies. Autoantibodies specifically attack proteins that are found in the nucleus of the cell. The ENA blood test screens for the following autoantibodies:

• Anti-RNP
• Anti-Sm
• Anti-SS-A
• Anti-SS-B
• Scl-70
• Anti-Jo-1

The ENA blood test is done on a sample of blood drawn from a vein in the arm. There aren't any special requirements or preparation needed when taking the test.

The results of an ENA blood test are either positive or negative for each autoantibody. Normally, when the immune system is functioning properly, there are few, if any autoantibodies in the blood. The presence of an autoantibody in significant quantity, along with the symptoms of an improperly functioning immune system, indicates a specific auto-immune disease.

If the ENA blood test shows the presence of Anti-RNP, which is the ribonucleoprotein antibody, the most likely cause is mixed connective tissue disease. The Anti-Sm, also known as the Smith antibody, is present in individuals that have systemic lupus erythematosus. The presence of Anti-SS-A and Anti-SS-B indicates Sjögren's syndrome. If the ENA blood test shows the presence of Scl-70, then the individual most likely has Scleroderma. If the blood contains Anti-Jo-1, then the probable cause is polymyositis.

Mixed connective tissue disease is an auto-immune disease that causes fatigue, muscle pain, and interrupted blood flow to extremities. Systemic lupus erythematosus is characterized by joint pain and inflammation. The disease affects the kidneys, heart, and lungs. Sjögren's syndrome is an auto-immune disease in which the immune system attacks the tear and salivary glands. It causes dry mouth and dry eyes. Scleroderma is a disease which causes the tightening of the skin and hardening of connective tissue. Polymyositis is a connective tissue disease characterized by muscle weakness and inflammation.

1. "ENA Panel." Lab Tests Online. American Association for Clinical Chemistry. 24 Nov. 2010. Web 8 Dec. 2010.

2. "Laboratory Tests - ENA." Park Nicollet. Park Nicollet Health Services. Web 8 Dec. 2010.