ANA test: measured in titers

An antinuclear antibody (ANA) test measures the amount and pattern of antibodies in your blood that work against your own body (autoimmune). The results of an ANA test are usually given in titers. A titer is a measure of how much the blood sample can be diluted before the presence of the antibodies can no longer be detected. [ Basically the titer its a ratio referring to a concentration of antibodies ] For example, a titer of 1 to 40 (1:40) means that antibodies can be detected when 1 part of the blood sample is diluted by up to 40 parts of a salt solution (saline). A larger second number means there are more antibodies in the blood. Therefore, a titer of 1 to 80 indicates more antibodies in the blood than a titer of 1 to 40. There are different subtypes of ANA which may have a range of normal values. Normal values may vary from lab to lab. Results will usually be available in about 1 week. Antinuclear antibodies, may have Normal titer of 1:40 or less.


What does the ANA test result mean?

True Positive ANA

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.

About 95% of SLE patients have a positive ANA test result. If a patient also has symptoms of SLE, such as arthritis, a rash, and autoimmune thrombocytopenia, then he 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 anti-dsDNA and anti-SM, 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.

A positive result on the ANA also may show up in patients with Sj√∂gren’s syndrome, Scleroderma, 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.

Negative ANA

A negative ANA result makes SLE an unlikely 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.

Aside from rare cases, further autoantibody (subset) testing is not necessary if a patient has a negative ANA result.

False positive results

The ANA test is said to be false positive when a person tests positive but does not have any other features of autoimmune disease . This situation occurs more often in women and elderly people. Certain medications, such as hydralazine, isoniazid, procainamide, and some anticonvulsant medications increase the chances of having a positive ANA test

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