Characteristics of an Antinuclear Antibody Test

The antinuclear antibody test is particularly useful for people with lupus but it can also guide the diagnosis of other autoimmune diseases. We'll explain what it consists of in this article.
Characteristics of an Antinuclear Antibody Test

Last update: 24 September, 2021

An antinuclear antibody test is one of the most commonly used tests in medical consultations, both in rheumatology and in family medicine. Physicians perform it in patients that may have an autoimmune disease.

Autoimmune diseases are those that occur because the immune system recognizes its own tissues as foreign. Lupus, scleroderma, and rheumatoid arthritis are some examples.

Many of these conditions have similar symptoms so an antinuclear antibody test can help determine an accurate diagnosis. Today’s article will explain what it consists of and how doctors perform it.

Antinuclear antibodies

Antibodies are proteins produced by the white blood cells of the immune system. They’re responsible for recognizing molecules of external agents that are potentially aggressive for the organism. Infectious microorganisms, for example.

Thus, antibodies recognize the foreign particles and trigger responses against the infection. In other words, they set in motion the inflammatory process. The problem is the body sometimes synthesizes the wrong antibodies. This is because the immune system mistakes the normal molecules in the body as foreign. Hence the term “autoantibodies.”

According to a publication of the American College of Rheumatology, antinuclear antibodies (ANA) are those that attack the proteins in the nucleus of one’s own cells. Almost everyone has autoantibodies in small amounts.

However, an extreme concentration of these antinuclear antibodies is usually indicative of an autoimmune disease. They’re, therefore, one of the main aspects in the diagnosis of these conditions.

Doing an antinuclear antibody test

This test is relatively simple, at least for the patient. A nurse or lab technician draws a blood sample. Then they place a kind of compressive bandage on the arm to easily locate the vein. They insert the needle and withdraw a small amount. The patient doesn’t have to fast beforehand.

The patient then presses the puncture site for a few minutes with sterile gauze. The blood is sent to the laboratory to analyze with the fluorescent antinuclear antibody test.

This method basically stains the antibodies so these are visible under a microscope and be able to determine the intensity of their fluorescence and pattern.

A lab technician doing an antinuclear antibody test.
This is a lab test done after drawing a blood sample from a patient.

Why take an antinuclear antibody test?

The antinuclear antibody test guides the diagnosis of autoimmune diseases. When there’s suspicion of lupus, rheumatoid arthritis, or scleroderma, for example.

According to specialists at the Mayo Clinic, the antinuclear antibody test doesn’t specifically confirm the diagnosis. However, it does help guide the process and protocol. This is useful because many disorders have very similar and nonspecific symptomatology — such as fatigue and joint pain.

Doctors rule out a diagnosis when this test is negative. In turn, it’s indicative of autoimmune disease if the results are positive.

This test is particularly sensitive for evaluating lupus. In fact, more than 95% of people with the disease have a positive result. However, many healthy people (up to 15%) have striking titers.

Test results and interpretation

The interpretation of the antinuclear antibody test is complex and requires experience. The result is positive when the antinuclear antibodies are present. However, as mentioned above, this isn’t immediately and directly synonymous with disease.

In fact, the result is usually positive in women over 65 years of age without having any autoimmune condition, as a publication in Encyclopaedia Medica points out. False positives can also occur when taking certain drugs.

Therefore, one must consider the results in the context of the patient’s clinical picture. In addition, a doctor may order other tests to help confirm the diagnosis or to obtain further information.

Titers are the quantifiers of antibodies and specialists obtain them by creating dilutions of the antibodies in saline solutions. That is, they mix the blood and create different tubes depending on the dilution (e.g. 1 part blood with 40 parts saline).

A blood sample diluted in 160 parts of saline still obtaining antibody values means the result is positive. In addition, the test also reports the distribution pattern of the antibodies.

Possible risks and errors

The main risks of the antinuclear antibody test derive from misinterpretation. When a negative result is obtained, it is considered that there are no autoantibodies. Therefore, autoimmune diseases are almost ruled out.

However, they must consider a few things if the result is positive. For instance, up to 37 % of healthy people over 65 years of age have them. In addition, viral and bacterial infections can also cause false positives. The same applies to certain types of cancer and to drug consumption.

It’s essential for the antibody titer to correlate with the clinical and physical examination. Physicians often prescribe total immunoglobulin quantification tests or a complement test to reduce the possibility of error and to compare results.

A woman with lupus.
Lupus is the classic disease associated with antinuclear antibodies but one can study other autoimmune disorders with this method.

The antinuclear antibody test is indicative

This test is for detecting antibodies directed against substances in the body’s own cells. Such molecules are usually present in high concentrations in diseases such as lupus.

However, to obtain a reliable result one must interpret the results in the context of the patient’s symptoms. It’s actually important to do other tests as well as checking family history.

This is because it’s possible for a healthy person to obtain a positive result and it doesn’t necessarily imply a disease. In fact, antinuclear antibodies may also elevate in other circumstances.

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