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Lupus - ANA test

What is ANA test?
ANA stands for Anti nuclear antibodies & are antibodies produced by the immune system against the nuclei of cells. The cell is made up of a nucleus & the surrounding cytoplasm. These antibodies directed against the nucleus of the cell are the main antibodies seen in SLE.
ANA test is best performed by immunofluorescence technique. In the immunofluorescent microscopy method, the patient's serum is incubated with cells attached to a microscope slide. ANAs if present in the serum attach to the nuclei of the cells on the slide. These ANAs attached to the nuclei can then be seen after addition of immunofluorescent dye. This is one of the best method to detect ANA. ELISA method is also used to detect ANAs.

A Rheumatologist looks at the titer as well as pattern when interpreting the report. The titer indicates the amount of dilutions performed till the ANA are not seen in the patient's serum. Hence a dilution of 1:320 is more than 1: 40 or 1:160. A higher titer thus indicates a strongly positive test. A titer of 1:40 or less is generally regarded as negative test report.

Pattern of the test is examined under the microscope. The antibodies are directed against different parts of the nucleus. This makes the ultimate difference in the pattern as seen under the microscope. The common pattern seen in lupus is called 'homogenous' pattern.

Though ANA is positive in most of the cases of Lupus, it is also positive is other autoimmune diseases like Scleroderma, Mixed connective tissue diseases. At the same time, many healthy individuals, especially elderly individuals have a (false) positive ANA test. Hence, the final interpretation of the ANA test is best left to the Rheumatologist.
Can a positive ANA occur in a normal individual?
Yes. 5% on normal individuals can have a positive ANA test. The chances are higher if you are elderly or a relative of a lupus patient. The titer in these cases is generally less than 1:40.
Can a patient of SLE ever be ANA negative?
Yes. ANA can rarely (1%) be negative in a patients of active SLE. Patients on regular treatment with controlled disease activity may also have a negative ANA.
What is a LE cell test?
LE cell test is a blood test used in 1960s to look for ANAs. With the availability of advance methods to measure ANA, this method is hardly ever used nowadays.

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Also Read:
Serum C3, C4 test
Lupus Nephritis
Drug Induced Lupus

Created on: April 2007
Last updated on: Feb 2015
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