Background

Antinuclear Antibody (ANA) tests detect antibodies present in serum. It binds to autoantigens, which are found in mammalian cell nuclei. IgG forms most of the antibodies. IgA and IgM also detected. The ELISA method includes the interaction of antibodies which are present in the serum sample. It was prepared with Ag and the addition of an antibody which forms a complex and produce a color change. It produces an optical density range or a photometric scale. It can be read as an equivocal, a   positive, or negative.

The IFA method is used in laboratories. It uses Hep-2 cell line. It is a substrate of human cell line. An antigen and antibody complex binds to the fluorescent labelled Ab.

ANA is used in different diseases like collagen or connective tissue diseases like systemic lupus erthyematosus (SLE), Sjögren syndrome, mixed connective tissue disorder, CREST syndrome, scleroderma, polymyositis, rheumatoid arthritis (RA), and dermatomyositis.

Some studies have shown that there is a connection between corona virus and ANA. As per the study of De Santis, about 35 patients have COVID-19, and 20 patients had ANAs.

Medications like phenytoin, procainamide, penicillin, hydralazine, chronic liver disease, neoplasms, viral diseases, and chronic infections are the result of reduced titer value of ANA. Healthy individuals and elder people may have reduced titer value. Patients who have SLE and are on steroids may get negative results. Patients who have SLE may slow have negative test result.

Patients who have SLE, levels of ANA can alter over time. It is because of the immunosuppressive agents and natural history of disease. There is no conditions which is occur in which this test must not be conducted.

Indications/Applications

The ANA test is performed:

To diagnose SLE

To screen the other autoimmune disease like scleroderma, Sjögren’s syndrome, polymyositis, dermatomyositis, mixed connective tissue disease (MCTD).

To monitor the activity of disease

To evaluate the overlap syndrome like lupus-scleroderma overlap

The symptoms of autoimmune disease are fever, fatigue, joint pain, blisters, changes in skin color, rash, swelling, stiffness, muscle pain.

Reference Range

The normal range of ANA is negative by the method of ELISA.

If the result of ELISA is abnormal or equivocal, the sample is titered by using the method of immunofluorescence (IFA) on the Hep-2 cells. Any range which is lower than or equal to less than 1.0 IU or 1:40 dilution is negative.

The rate of the positivity of ANA screening test is below:

Drug-induced lupus erythematosus: 100%

Mixed connective tissue disease: 100%

Sjögren syndrome: 80%

Systemic lupus erythematosus: 95 to 100%

Polymyositis dermatomyositis: 49 to 74%

Rheumatoid arthritis: 40 to 60%

Scleroderma: 60 to 95%

Normal: Below 4%

Interpretation

The negative range indicates that it is unclear that a connective tissue disease is diagnosed. Level which is more than or equal to 1:160 is positive. The degree of positivity is below:

Negative: Below or equal to 1.0 U

Weakly positive: 1.1 to 2.9 U

Positive: 3.0 to 5.9 U

Strongly positive: More than or equal to 6.0 U

Many connective tissue diseases are linked with a many frequency of positivity of ANA. A positive titer is linked with an antibody pattern. Interpretation of pattern is random. It is not specific to particular condition of disease. A positive test result does not prove the disease. It enhances the symptoms and signs, specific antibody tests, and radiographic and histopathologic results.

Titer value may vary from laboratory to laboratory from ranges to 1:32 to more than 1:5120 on the same sample.

Conditions which can cause a positive test result of ANA are:

SLE

Sjögren’s syndrome

Rheumatoid arthritis (RA)

Scleroderma

Polymyositis

Mixed connective tissue diseases

Dermatomyositis

Juvenile chronic arthritis

Polyarteritis nodosa

Autoimmune hepatitis

The ANA test result is positive if the patient has any of these conditions like:

Thyroid diseases like Grave’s disease, Hashimoto’s thyroiditis

Inflammatory bowel disease

Raynaud’s syndrome

Liver disease like primary biliary cirrhosis, autoimmune hepatitis

Lung diseases like idiopathic pulmonary fibrosis

Viral infections

Cancer

The false positive result will get in the following conditions:

Women whose age is older than 65 years

Patient who take anti-seizure or blood pressure medications

Who have infections like tuberculosis or mononucleosis

Collection And Panels

Sample: blood serum

Sample collection container: red top tube

Sample volume: 7 mL

Sample storage instructions: Store the sample at 48ºC for 72 hours or -20 ºC in refrigerator. Acetone-fixed substrate slides are chosen than the methanol and ethanol fixation in IFF. This is because of the latter is removed SSA antigen. This test result is not affected by any environmental conditions.

Panels:

Anti-dsDNA test, Anti-Sm test, Anti-RNP test, Anti-La/SSB Anti-Ro/SSA test, Anti-centromere test, Anti-Scl-70 test, Anti-Jo-1 test

References

https://www.ncbi.nlm.nih.gov/books/NBK537071/