Arthritis and Rheumatism

ANA vs. ENA Test

ANA - Anti-Nuclear Antibody Test

ANA is an acronym for Anti-Nuclear Antibody. The ANA blood test is a nonspecific screen for autoimmune stimulation. Its use in Rheumatology is to screen for Connective Tissue Diseases; however, the presence of an ANA is not isolated to rheumatic diseases.
How the test works

An ANA is performed by exposing cells (most commonly, a Human Epithelial, type 2 cell (HEp-2)) to an individual’s blood and looking for a specific interaction with components of the cells’ nucleus.
What the results mean, and what they don't

The specific antigen within the nucleus that causes the elevation of the ANA is not known with the ANA test alone. Although an elevated ANA can be found in over 95% of individuals with Systemic Lupus Erythematosus, the test's main disadvantage is that it is very nonspecific. It may be elevated in other connective tissue diseases such as Scleroderma or Sjogren's Syndrome. An elevated ANA may also be elevated in up to 30% of "normal persons."¹ An ANA, therefore, should not be used in isolation to diagnose connective tissue diseases. Rather, the test should be considered in conjunction with other clinical features to assist in diagnosis of certain rheumatic diseases.

ENA - Extractable Nuclear Antigens Test

ENA is an acronym for Extractable Nuclear Antigens.
How the test works

ENA panel detects antibodies to specific antigens within the nucleus that might be responsible for the elevated ANA.
What the results mean

By knowing the specific antigen that is elevated, your physician may be able to better interpret your clinical data to arrive at a diagnosis.

Comparing the results

Of note, it is not uncommon to have an elevated ANA and normal ENA panel. Also of note, the components of an ENA panel may vary from laboratory to laboratory.

References

1. Guidelines for clinical use of the antinuclear antibody test. In: Klippel, JH (ed). Primer on Rheumatic Diseases, 12th Edition. Atlanta: Arthritis Foundation, 2001; p 654.