ANA stands for Antinuclear Antibody.  As the name implies, the test is designed to identify antibodies in the blood that are capable of attacking the inner part (nucleus) of a patient’s cells.  This phenomenon is the hallmark of autoimmune disease.

The body normally makes antibodies (specially configured proteins) as part of the body’s defence against infection. For example, when we are given shots to prevent illnesses such as measles, mumps, or polio, the body is induced to create antibodies against these viruses.  If we are then exposed to these infections, our antibody molecules seek out the virus, attach themselves to it and trigger a series of chemical reactions that destroy the virus.

In autoimmune disease, the immune system is flawed and instead of making antibodies only against noxious foreign substances, it makes antibodies against normal human cells.  The patient’s own cells then suffer the same fate as an unwanted virus.  This results in chronic damage to tissues such as the kidney, joints, blood vessels, liver, etc.

The most common autoimmune disease is SLE (Systemic Lupus Erythematosus).  It is also called Disseminated Lupus Erythematosus.  The name is an old term that refers to the fact that some people with SLE have a red rash (erythema) over their nose and cheeks that gives a wolf-like (lupus) appearance.  The word “systemic” or “disseminated” refers to the fact that the disease affects many parts of the body.

There are several significant signs and symptoms that suggest the presence of SLE.  The American College of Rheumatology has developed 11 criteria for making this diagnosis.  A patient must have at least four of these present simultaneously or individually over a period of observation, before the diagnosis of SLE can be considered.  The criteria are:

Malar (cheek) rash

Discoid rash (a rash with a particular configuration)

Photosensitivity (skin sensitive to light)

Mouth ulcers

Arthritis

Serositis (pleuritis or pericarditis: fluid on the lungs or the heart lining)

Kidney disease (persistent proteinuria or cellular casts)

Neurological disorder (seizures or psychosis)

Hematological disorder (anemia, leukopenia [low white cell count] or lymphopenia [low lymphocyte count] on two or more occasions, and/or thrombocytopenia [low platelet count] )

Immunological disorder (abnormal  anti-DNA or anti-Sm test)

Abnormal ANA

The ANA test is carried out by mixing the patient’s blood serum on a slide covered with cells and is then examining the preparation with a special microscope.  If autoantibodies are present they will be seen to fix themselves to parts of the cell nucleus.

A negative ANA rules out SLE (except that negative results will be found occasionally as the disease ebbs and flows between being active and quiescent).

Up to 30 % of all people will have slightly positive ANA tests (frequency increases with age).  In most cases, slight positives are of no significance.

High positive results are usually significant.  They may be due to SLE but may also be caused by certain drugs, Sjogren’s Syndrome, Scleroderma, Mixed Connective Tissue Disease, CREST syndrome, and a number of more unusual disorders.

Sorting out which condition is present is done by evaluating the clinical signs and symptoms, by studying the part of the cell nucleus that the antibodies attack, and by performing supplementary tests such as the ENA and antiDNA.