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ANA
tests
Antibodies are small proteins that your body makes to help defend
itself against pathogens like viruses. If the body is exposed to
a virus or some other dangerous element, B cells of the immune system
respond by producing antibodies that can bind to the protein antigens
that the virus contains. These antibodies are released into the
blood and when they find a cell which a virus has infected they
bind to the infected cell. This acts as a signal to other parts
of the immune system to target and destroy the cell and the virus
inside. Unfortunately, the immune system can get confused and it
can start producing antibodies that target protein antigens on the
body's healthy cells. When this happens an autoimmune disease can
develop. Which autoimmune disease develops depends on where the
protein antigens are expressed in the body.
The abbreviation ANA stands for "anti-nuclear antibody"
and an ANA test looks for the presence of antibodies in your blood
that target components of a cell nucleus. Some types of autoimmune
disease in which antinuclear antibodies are produced involve hair
loss as a symptom. Different patterns and concentrations of antinuclear
antibodies can help determine whether an autoimmune disease has
developed and what kind of autoimmune disease it is. However, an
ANA test alone cannot diagnose a specific disease.
An ANA test may be ordered if a patient complains of symptoms including
painful or swollen joints, unexplained fever, extreme fatigue, hair
loss and a red rash. These symptoms can be an indicator of several
inflammatory disorders. The ANA test is primarily used to help diagnose
systemic lupus erythematosus and drug-induced lupus, and may also
be positive in cases of scleroderma, Sjögren’s syndrome,
Raynaud’s disease, juvenile chronic arthritis, rheumatoid arthritis,
antiphospholipid antibody syndrome, autoimmune hepatitis, and many
other autoimmune and non-autoimmune diseases. A number of medications
(including chlorpromazine, methyldopa, isoniazid, lithium, hydralazine
(Apresoline), procainamide (Procan, Pronestyl), anticonvulsant drugs
such as Dilantin, some antibiotics including isoniazid, penicillin,
and tetracycline, birth control pills, and some diuretics) and other
chronic diseases such as liver or lung disease, or a chronic infection,
can cause a positive ANA test. Because the ANA test result may be
positive in a number of these diseases, A thorough medical history,
physical exam, and other tests are needed to identify which particular
disease is involved.
The main reason for doing an ANA test is when Systemic Lupus Erythematosus
(SLE), commonly known as "lupus", is suspected. In this
condition, a mixture of diffuse and patchy hair loss can be one
of the symptoms. Less than 2% of people with lupus have negative
ANA test results that remain negative even when the test is repeated
several times. Most people who have lupus but who have negative
ANA tests have a form of lupus in which the main symptoms are just
a skin rash and sometimes associated hair loss. This form of lupus
is called discoid or cutaneous lupus, and it is not considered to
be systemic lupus. Almost all people with lupus will have a positive
ANA test if the test is repeated. A confirmed diagnosis of SLE is
based on a person's symptoms, the results of a physical exam, and
the results of certain lab tests. SLE cannot be diagnosed by the
results of the ANA test alone.
How
an ANA test is done
An ANA test is done on a blood sample. Those with blood clotting
disorders or on medications that thin the blood like aspirin or
warfarin (Coumadin) should tell the doctor before any blood sample
is taken - it may not be appropriate to give a blood sample.
The individual taking the blood sample will wrap an elastic band
around your upper arm to temporarily stop the flow of blood through
the veins of your arm. This makes it easier to put the needle into
a vein properly because the veins below the band get larger and
do not collapse easily. The needle site is swabbed with disinfectant
and the needle is inserted. You may feel a brief sting as the needle
goes in and some minor discomfort while the needle is in the vein.
How much depends on the skill of the person drawing the blood, the
condition of your veins, and your sensitivity to pain.
More than one needle may be needed if the needle does not get placed
correctly or if the vein cannot supply enough blood. When the needle
is properly placed in the vein, a collection tube will be attached
to the needle. The collection tube has a vacuum inside so when it
is attached to the needle it "sucks" the blood into the
tube quite quickly. Sometimes more than one tube of blood is collected.
When enough blood has been collected, the band around your arm will
be removed. A sterile gauze pad or cotton ball is placed over the
puncture site as the needle is withdrawn. Pressure is applied to
the puncture site for several minutes to stop the bleeding and a
bandage may be added afterwards. You might develop a small bruise
at the puncture site. You can reduce the risk of bruising by applying
pressure to the puncture site for several minutes after the needle
is withdrawn. Rarely, the vein may become inflamed (phlebitis) after
the blood sample is taken. Phlebitis is usually treated with a warm
compress applied several times daily.
The original ANA test involved removing the blood cells from the
blood sample by centrifugation and then making several different
diluted samples of serum using a salt solution. These dilutions
would each be tested on cultured cells by a technique known as an
indirect immunofluorescent assay. Any antibodies in the dilutions
that were specific to the cell proteins would bind to the cells.
A second, man-made antibody that binds to all human antibodies would
be added and this antibody is conjugated to fluorescent particles.
If any serum antibodies bind to the cells, the second antibody would
bind to them and fluorescence will show where the bound antibodies
are under a microscope. More recently this test has been superseded
by a superior technique called an enzyme-linked immunosorbent assay
(ELISA). The ELISA method is less likely to produce a false-positive
ANA result than the IFA method. It works in much the same way as
an IFA test except the test is done on purified nuclear proteins
in solution rather than on actual cells. This also bring the advantage
that the serum sample can be tested against several specific nuclear
proteins simultaneously. Different proteins are targeted in different
inflammatory conditions so the pattern of test results can help
diagnose specific diseases with greater confidence.
How
to read the ANA test result
The doctor may simply tell you whether the result was positive
or negative which suggests a clear cut result. However, if you are
given the actual test result data sheet you will see that an ANA
test result is reported as a "titer". A titer is a measure
of how much the blood sample can be diluted before the activity
of the antibodies can no longer be detected. A titer of 1 to 80
(1:80) means that antibodies could be last detected when 1 part
of the blood sample was diluted by 80 parts of a salt solution.
A larger second number indicates that the antibodies are present
in greater concentration. So a titer of 1 to 320 indicates a much
higher concentration of antibodies in the blood than a titer of
1 to 80.
Some perfectly healthy people do have slightly positive ANA tests.
Aging can affect the levels of antinuclear antibodies, and some
older adults (5% to 40%) may have mildly elevated levels. However,
whilst there are some antinuclear antibodies in the blood, there
are not enough for it to be a problem. People who are healthy but
have a positive ANA test will see they have a low titer on their
test result. A positive result where the titer is less than 1 to
40 (varies from lab to lab) is not a problem. A positive test result
where the titer is more than 1 to 40 may be cause for concern. The
higher the titer goes the more clear cut the positive result. The
actual value at which the test is deemed positive with confidence
varies from lab to lab but in general above 1 to 80 suggests a problem
is very likely. Other tests are then required along with a full
medical to determine how much of a problem.
What
the ANA test result means
A positive ANA titer may mean that the person tested has lupus,
but it is not conclusive proof. Almost all people with lupus have
a high ANA titer. However, other conditions may also cause a high
ANA titer. For example, about 30% to 40% of people with rheumatoid
arthritis also have a high ANA titer. So to be confident that an
individual has lupus, other indicating factors must also be present
such as arthritis, a rash, and autoimmune thrombocytopenia (a low
number of blood platelets).
If needed, two subset tests for antibodies against purified nuclear
proteins dsDNA and SM, can help to show that the condition is lupus.
If anti-dsDNA antibodies are found, this supports the diagnosis
of lupus. Higher amounts of anti-Sm are also more specific for lupus.
A positive ANA can also mean that the patient has drug-induced lupus.
This condition is associated with the development of autoantibodies
to histones in cell nuclei. An anti-histone test can be given to
support the diagnosis of drug-induced lupus. Any drug induced lupus
can be reversed by stopping use of the drug.
Other conditions in which a positive ANA test result man be seen
include:
Sjögren’s syndrome: Between 40% and 70% of patients with
this condition have a positive ANA test result. If Sjögren’s
syndrome is suspected, your doctor may want to test for two subsets
of ANA, looking for antibodies against the ribonucleoproteins SSA
and SSB. The frequency of antibodies to SSA in patients with Sjögren’s
can be 90% or greater. The other common symptoms of Sjögren’s
syndrome that the doctor will look for include persistent dry eyes
and dry mouth.
Scleroderma: About 60% to 90% of patients with scleroderma have
a positive ANA finding. In patients who may have this condition,
the subset tests can help distinguished two forms of the disease,
limited versus diffuse. The diffuse form is more severe. Limited
disease is most closely associated with an anti-centromere pattern
of ANA staining (anti-centromere test), while the diffuse form is
associated with autoantibodies to the protein Scl-70 (anti-Scl-70
test).
A positive result on the ANA test may also show up in patients
with Raynaud’s disease, juvenile chronic arthritis, or antiphospholipid
antibody syndrome, but a doctor needs to rely on clinical symptoms
and clinical history for diagnosis of these conditions.
A negative ANA test result makes SLE an unlikely diagnosis. Unless
an error in the testing is suspected, it is not necessary to immediately
repeat a negative ANA test. However, because autoimmune diseases
change over time, it may be worthwhile to repeat an ANA test in
the future.
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test references
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