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ANA Test for Lupus
What is ANA?
ANA stands for
anti-nuclear antibody. Put simply this test is looking for a
protein in your blood that destroys the
nuclei of your
cells. There are also various sub-types of this test such
as Anti-dsDNA, Anti-Ro, Anti-Sm, and others. These are
discussed on other pages that can be found on the
Lupus Diagnosis/Tests
page.
Why it is done?
This test is
currently the most sensitive test used for diagnosing SLE.
97% of people with SLE will have a positive ANA. This test
can also be helpful in diagnosing Drug-induced Lupus. A
positive ANA however does NOT confirm a Lupus diagnosis on it's
own. At least 3 others of the
11 criteria
established by the American Rheumatism Association must
be present as well as a positive ANA to confirm a Lupus
diagnosis. More about other possible causes of a positive
ANA later in this document.
How is it done?
Laboratories take a
small sample of blood, usually from the arm. The results
are expressed with both a titer and a pattern. The titer
is a ratio that expresses the number of times the technician had
to dilute the plasma from the blood before the antibodies could
no longer be detected. There are different patterns of a
positive ANA; rim (sometimes called peripheral), homogenous
(sometimes called smooth), speckled, diffuse, nucleolar, and
centromere.
Normal Levels:
(normal values may vary from lab to lab)
Titers of 1:20 or
1:40 or less are generally considered normal depending on the
lab and methods used to conduct the test.
What a negative ANA
means:
A negative ANA
argues pretty strongly against Lupus but it does not completely
rule it out. Infrequent cases of SLE patients with
negative ANAs can be found when positive Anti-Ro (SSA) or
antiphospholipid antibodies are present.
What a positive ANA
means:
A positive ANA does
not automatically mean Lupus, once again other clinical findings
must be taken into account. The reason for this is because
a positive ANA can also be found in many other autoimmune
diseases such as Multiple Sclerosis, Autoimmune Thyroiditis,
Scleroderma, Sjogren's Syndrome, Autoimmune Hepatitis, and
Rheumatoid Arthritis. This test can also be positive in
people with some infectious diseases like mononucleosis, chronic
hepatitis, malaria and lepromatous leprosy. There are
certain drugs such as isoniazid, procainamide,
chlorpromazine, and hydralazine can cause a positive ANA also.
30-40% of first degree relatives of SLE patients will have a
positive ANA and no symptoms. Finally, as many as 20% of
completely healthy individuals will also have a positive ANA.
What the titer
number means:
As stated before
the titer is a ratio that expresses the number of times the
technician had to dilute the plasma from the blood before the
antibodies could no longer be detected. In other words, a
titer of 1:40 would mean that the antibodies were last detected
when 1 part of the blood was diluted with 40 parts of either
water or saline. The higher the second number the higher
the concentration of antibodies. Since the amount of
dilution fluid is doubled the titers can increase rapidly from
1:40 to 1:80 to 1:160 to 1:320 to 1:640 and so on.
Antibodies fluctuate in concentration during the course of
disease and a high or low titer does NOT indicate the level of
disease activity and can not reliably be used to determine
disease activity level. However, the higher the titer, the
more likely an autoimmune disease is present.
What the pattern
means:
Rim / Peripheral - found
almost exclusively in people with SLE
Homogenous / Smooth - found
in high titers in SLE also found in Drug-Induced Lupus, and
other autoimmune diseases, also the most commonly found pattern
in healthy individuals
Speckled - found in SLE,
mixed connective tissue disease, Sjogren's Syndrome, Scleroderma
Diffuse - non-specific
pattern
Nucleolar - found in
Scleroderma, CREST Syndrome, systemic sclerosis, and sometimes
SLE or Rheumatoid Arthritis
Centromere - found in PSS with
CREST Syndrome, polymyositis, Raynaud's Syndrome
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