What is being tested?

The Antinuclear Ab test identifies the presence of antinuclear antibodies (ANA) in the blood. ANA is a group of special antibodies produced by the patient's immune system when it fails to adequately distinguish between ‘self’ and ‘non-self’. These autoantibodies may attack the body’s own cells, causing signs and symptoms such as tissue and organ inflammation, joint and muscle pain, and fatigue. The presence of ANA can be a marker of an autoimmune process and is associated with several autoimmune disorders but is most commonly seen in the autoimmune disorder systemic lupus erythematosus (SLE).

ANA may also more commonly appear in normal people with various patterns. By the time we are 70, up to 30% of women and 20%  of men are ANA positive.

How is it used?

The ANA test is ordered to help screen for autoimmune disorders and is most often used as one of the tests to diagnose systemic lupus erythematosus (SLE). Depending on the patient’s symptoms and the suspected diagnosis, ANA may be ordered along with one or more other autoantibody tests. Other laboratory tests associated with presence of inflammation, such as erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) may also be ordered. ANA may be followed by additional tests that are considered subsets of the general ANA test and that are used in conjunction with the patient’s clinical history to help rule out a diagnosis of other autoimmune disorders.

When is it requested?

The ANA test is ordered when a patient shows signs and symptoms that are associated with SLE or another autoimmune disorder. It may also be ordered when a patient has been diagnosed with an autoimmune disorder and the doctor suspects that the patient may have developed an additional autoimmune disorder. Patients with autoimmune disorders can have a wide variety of symptoms such as low-grade fever, joint pain, fatigue, and/or unexplained rashes that may change over time.

What does the result mean?

ANA tests are performed using different assays (indirect immunofluorescence microscopy or by enzyme-linked immunoabsorbent assay - ELISA) and results are reported as a titre with a particular type of immunofluoroscence pattern (when positive). Low-level titres are often considered negative, while increased titres, such as 1:320, are positive and indicate an elevated concentration of antinuclear antibodies. Even high titre antibodies can be seen on those with no evidence of autoimmune disease.

ANA shows up on indirect immunofluorescence as fluorescent patterns in cells that are fixed to a slide that is evaluated under a microscope. Different patterns are associated with a variety of autoimmune disorders. Some of the more common patterns include:

• Homogenous (diffuse) - associated with SLE and mixed connective tissue disease
• Speckled - associated with SLE, Sjogren’s syndrome, scleroderma, polymyositis, rheumatoid arthritis, and mixed connective tissue disease
• Nucleolar - no definite disease association. In scleroderma, this pattern is more likely to be present than others (~70% of systemic scleroderma patients have positive ANA’s)
• Outline pattern (peripheral) - associated with SLE
• DFS70: This pattern termed dense fine speckled antibodies is not associated with any autoimmune disease. It needs to be confirmed with ENA testing

An example of a positive result might be: ‘Positive at 1:320 dilution with a homogenous pattern.’

A positive ANA test result may suggest an autoimmune disease but further specific testing is required to assist in making a final diagnosis. ANA test results can be positive in people without any known autoimmune disease. While this is not common, the frequency of a false positive ANA result increases as people get older.

Also, ANA may become positive before signs and symptoms of an autoimmune disease develop, so it may take time to tell the meaning of a positive ANA in a person who does not have symptoms. Most positive ANA results don't have significance, so physicians should reassure their patients but should also still be vigilant for development of signs and symptoms that might suggest an autoimmune disease. Perhaps as few as one in 400 people with a positive ANA will have SLE.

100% of SLE patients have a positive ANA test result at diagnosis using modern screening tests. Over time the ANA will fluctuate and may become negative on treatment. If a patient also has symptoms of SLE, such as arthritis, a rash, and autoimmune thrombocytopenia, then he or she probably has SLE. In cases such as these, a positive ANA result can be useful to support SLE diagnosis. Two subset tests for specific types of autoantibodies, such as double stranded DNA Ab and ENA, may be ordered to help confirm that the condition is SLE.

A positive ANA can also mean that the patient has drug-induced lupus. This condition is associated with the development of autoantibodies to histones, which are water soluble proteins rich in the amino acids lysine and arginine. An anti-histone test may be ordered to support the diagnosis of drug-induced lupus. Anti-histone antibodies are also seen in non-drug induced SLE.

Other conditions in which a positive ANA test result may be seen include:

• Sjögren’s syndrome: Most patients with this condition have a positive ANA test result. While this finding supports the diagnosis, a negative result does not rule it out. The doctor will want to test for two subsets of ANA: Anti-SSA (Ro) and Anti-SSB (La). The frequency of autoantibodies to SSA in patients with Sjögren’s is 100%.
• Scleroderma: About 60% to 90% of patients with scleroderma have a positive ANA finding. In patients who may have this condition, ANA 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 a pattern of ANA immunofluorescent staining called the anticentromere pattern (and the anticentromere test), while the diffuse form is associated with autoantibodies to the anti–Scl-70 as well as other antibodies.
• A positive result on the ANA also may show up in patients with Raynaud’s disease, rheumatoid arthritis, dermatomyositis, mixed connective tissue disease and other autoimmune conditions.

A doctor must rely on test results, clinical symptoms and the patient’s history for diagnosis. Because symptoms may come and go, it may take months or years to show a pattern that might suggest SLE or any of the other autoimmune diseases.

A negative ANA result excludes SLE as a diagnosis. It usually is not necessary to immediately repeat a negative ANA test, however, due to the episodic nature of autoimmune diseases, it may be worthwhile to repeat the ANA test at a future date.

In patients with some autoimmune disorders such as myositis, a negative ANA does not exclude the presence of specific antibodies.

Is there anything else I should know?

Some drugs and infections as well as other conditions mentioned above can give a false positiveresult for the ANA test.

About 3% - 5% of Caucasians may be positive for ANA and it may reach as high as 30% in healthy individuals over the age of 65.

Some medications may bring on a condition that includes SLE symptoms, called drug-induced lupus. When the drugs are stopped, the symptoms usually go away. Although many medications have been reported to cause drug-induced lupus, those most closely associated with this syndrome include hydralazine, isoniazid, procainamide and several anticonvulsants.

Common questions

• Why is it called ‘antinuclear’ antibody?

Antinuclear antibodies are autoantibodies that are directed against certain components found in the nucleus (centre) of a cell.

• My doctor told me my ANA test is positive but isn't sure if I have lupus. How can this be?

A positive ANA result means that you have a higher than ‘normal’ concentration of these antibodies. This is one of the tools in diagnosing lupus as well as several other autoimmune diseases, so a positive result may be related to lupus or another disease. Or you may simply have a higher than normal concentration of these autoantibodies that may not have any impact on your health. Even among people with lupus, these results can vary widely; one person can be in remission at a certain titre of ANA while another can be extremely ill at the same titre.

Autoimmune diseases often have a systemic effect on the body and are very complex by nature. Interpreting what these results mean for you is the work of your doctor. And your doctor may need to compare your test results as well as the severity of your symptoms over a period of time in order to make a definitive diagnosis. This additional time may also allow your doctor the opportunity to eliminate other possible causes for your symptoms.

• Is SLE the same thing as lupus?

There are actually several forms of lupus. SLE is the form that is most commonly referred to when someone mentions ‘lupus.’ Systemic lupus means that it can affect almost any organ or system in your body. This is the most severe form. There are other forms of lupus that are primarily limited to skin and their symptoms include rashes that may be found in many shapes and locations on the body. A butterfly-shaped rash is commonly seen on or near the face.

More information

RCPA Manual: Anti-nuclear antibodies