ENA vs ANA definition

ENA vs ANA definition

Definition ANA

ANA (antinuclear ANTIBODIES) classically are detected by immunofluorescence. Thus they are named after their place where they bind the antigens - in the nucleus. It is a general name for all antibodies which react with nuclear antigens.
But in the practical termination of doctors ANA also can bind antigens in the cytoplasm (like Jo-1 and Rib-P).

Definition ENA

ENA (extractable nuclear ANTIGENS) are a wide spectrum of nuclear antigens, which can be eluated easily by salt extraction. ENA are usually commercially available rabbit or calf thymus extract (CTE). They commonly has been used for Ouchterlony assays, but can be used also in other methods than immunodiffusion. ENA for ELISA or RIA are also commercially available, but their purity is not known. Usually, recombinant nuclear antigens are not called ENA.

The diagnostically most important ENAs are the Sm antigens. Other ENAs are U1-snRNP, SS-A/Ro, SS-B/La, Jo-1, Scl-70, PM-1, Mi and Ku.

DNA, centromere proteins and histones don't belong to the group of ENAs, but are nuclear antigens.

ENA or ANA

In summary the term ENA is used for a special group of nuclear antigens, defined by the method of purification. ANA can bind to ENA but also to other nuclear antigens.

I think the term "ANA Screen" is more correct than "ENA Screen" (even if we used only ENA for coating), as we mostly use recombinant antigens, not extracted antigens from animal tissue. (Besides we screen for antibodies, not for antigens).

More difficult is the situation in France or other countries were the term ANA is only used for ANA detected by immunofluorescence. The laboratory is obliged to use immunofluroescence if the physician asks for an ANA Screen. Only if ENA is asked for, the laboratory has the possibility to use ELISA.

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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.