Antinuclear Factor (ANF), Antinuclear Antibody (ANA) and Its Significance
Antinuclear factor (ANF)
Sample
- This test is done on the serum of the patient.
- How to get good serum: Take 3 to 5 ml of blood in the disposable syringe or a vacutainer. Keep the syringe for 15 to 30 minutes at 37 °C and then centrifuge for 2 to 4 minutes to get the clear serum.
- No fasting or preparation is required.
Purpose of the test (Indications) for Antinuclear Factor (ANF)
- For the diagnosis of Systemic lupus erythematosus (SLE).
- Positive in other autoimmune diseases.
Precautions for Antinuclear Factor (ANF)
- Drugs may cause false-positive tests like aminosalicylic acid, chlorothiazide, procainamide, hydralazine, acetazolamide, penicillin, phenytoin sodium, and griseofulvin.
- Drugs may cause a false-negative test like steroids.
- This test may be positive after the viral infection and some chronic infections.
Pathophysiology of Antinuclear Factor (ANF)
Definition of Antinuclear factor:
- Antinuclear antibodies are produced in connective tissue diseases (autoimmune diseases ) against various antigens in the nucleus like RNA, DNA, histones, and ribonucleoprotein.
- Autoantibodies are directed against nuclear material (ANA) or against cytoplasmic material called anti-cytoplasmic antibodies.
The major anti-nuclear antigens are:
- DNA (double and single-stranded).
- Histones.
- Nuclear proteins.
- RNA
- 95% of SLE patients show ANA.
Some of the commonly used anti-nuclear antibodies (ANA) and their significance:
Type of the Anti-nuclear antigen and antibody (ANA) | ANA and their diagnostic value |
ssDNA (Anti-ssDNA) |
|
ds-DNA (Anti-dsDNA) |
|
|
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Anti-nuclear Smith (sm) antibody |
|
Anti-RNP antibody |
|
Antinucleolar antibody |
|
Anti-sNP antibody |
|
Anti-SS-A and Anti-SS-B |
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Histones (anti-histone antibodies) |
|
Cytoplasmic antigens (anticytoplasmic Ab RNA and others) |
|
Anti-centromere antibody |
|
Significance of anti-nuclear factor (anti-nuclear antibody – ANA):
- This ANA is not a specific test for SLE, so it has to be supplemented by other tests. But this is the most sensitive test detecting the SLE at almost >95% positivity.
- Fluorescent staining under an ultraviolet microscope shows different patterns and increases the specificity of this test.
- Fluorescent patterns show different staining in the nucleus, e.g.:
- The homogeneous pattern is seen in SLE and mixed connective tissue disease.
- Peripheral outline only is seen in SLE.
- The speckled pattern has been seen in other autoimmune diseases like SLE, Sjogren’s syndrome, Scleroderma, Rheumatoid arthritis., and mixed connective tissue disease.
- The nuclear pattern is seen in Scleroderma and Polymyositis.
Table showing the pattern of ANA (immunofluorescence staining) in various diseases:
Diseases | Homogenous pattern | Peripheral Pattern | Speckled pattern | Nucleolar pattern |
SLE | + positive | + positive | + positive | + positive |
Mixed connective disease | + positive | + positive | ||
Scleroderma | + positive | + positive | ||
Rheumatoid arthritis | + positive | |||
Sjogren’s syndrome | + positive | |||
Polymyositis | + positive | + positive |
- ANA is gamma globulin and belongs to more than one type of immunoglobulin.
- There are ANA-negative cases of SLE.
- Some believe that negative ANA excludes the SLE.
Diseases with positive antinuclear antibodies:
Diseases | Positivity of ANA % | another source of positivity % | Another source of positivity % |
---|---|---|---|
SLE | 95 | 90 to 100 | >95 |
Drug-induced lupus erythematosus | >95 | ||
Sjogren’s syndrome | 60 | 85 | 75 to 90 |
Scleroderma | 70 | 88 | 70 to 90 |
Dermatomyositis | 30 | 40 to 60 | |
Rheumatoid arthritis | 30 | 55 | Rare |
Polyarteritis | 10 | ||
Juvenile arthritis | 22 | ||
Mixed connective tissue disease | 100 | >95 | |
CREST syndrome | 70 to 90 |
Lab diagnostic role of Antinuclear Factor (ANF):
- Indirect immunofluorescence, where the patient serum (antibody) has combined with the cells.
- EIA technique may replace the indirect immunofluorescence.
- ANA has a sensitivity of 99%. A negative ANA test almost excludes the active SLE.
- This test may be positive in unrelated diseases of the patients.
- Around 20% of the normal population has a titer of 1:40.
- Around 5% of the normal population may have a titer of 1:160
- When the cutoff titer is 1:40, then specificity is around 80%.
- When the cutoff value is 1:160, then specificity is around 95%.
- ANA is nonspecific; individuals with increasing age show a false-positive result.
- 50% positive by the age of 80 years with a low titer.
- Procedure for the ANA:
- Take 5 to 10 mL of the blood of the patient.
- Traumatize the RBCs with the glass rod or glass beads.
- Incubate for 15 to 30 minutes at 37 °C.
- Centrifuge and make the smear from the buffy coat.
- Screen the slide to find the SLE cell (LE cell phenomenon).
Normal Antinuclear Factor (ANF) or ANA
Source 2
- These are negative.
- Negative at 1:20 dilution.
- When done with a dilution of the serum, then a titer of more than 1:32 is positive.
Source 4
- Negative by ELIZA and IFA method.
- If positive by IFA, the sample is titrated, and the pattern is reported.
- A strong positive result that is >3 on ELIZA and ≥1:160 by IFA now needs follow-up of specific autoantibodies.
Interpretations of Antinuclear Factor (ANF)
- A positive test does not confirm the disease because its low titers are seen in old and healthy normal people.
- It helps diagnose Autoimmune diseases, particularly Systemic lupus erythematosus (98%) but with poor specificity.
- This test is positive 30 to 50% in other autoimmune diseases such as Rheumatoid arthritis, Sjogren’s syndrome (70%) and Polymyositis, and other related diseases.
- Positive ANA without other S/S is not diagnostic.
- The high titer is often associated with SLE, and titer <1:160 is not diagnostic.
- The titer of <1:40 is considered negative.
- The titer of 1:40 to 1:80 is considered low positive.
- While titer of >1:160 is considered positive.
- 5% of the SLE cases show persistently negative results.
- ANA may become negative in remission of SLE.
- If ANA is negative, then SLE can be excluded.
The positive or increased level of ANA is seen in:
- SLE.
- Rheumatoid arthritis.
- Polyarteritis Nodosa
- Dermatomyositis.
- Sjogren’s syndrome.
- Other autoimmune diseases.
- Cirrhosis.
- Chronic hepatitis.
- Leukemia.
- Scleroderma.
- Multiple sclerosis.
- Infections.
- Malignancies.
- Fibromyalgia.
Antinuclear factor (ANF): Le cell phenomenon: Nucleus is pushed to the peripheryQuestions and answers:
Question 1: What is LE cell phenomenon.
Question 2: What is the significance of ANA for the diagnosis of SLE.
How long do you have to be off a l0 mg dose of prednisone in order to prevent a false negative in ANA test?
Usually, prednisolone will be out of your body in 7 to 10 days.