Blood tests and Antibodies

There is no single or set of blood tests which diagnose SLE.  There are however some blood tests which help confirm, together with the other signs and symptoms, the diagnosis of SLE.  Antibody tests are such tests.

What are antibodies?

Antibodies (Ab), also known as Immunoglobulins (Ig), are proteins produced by the B cells, a type of White blood cell called lymphocyte.  They are used by the immune system to identify and neutralize bacteria and viruses, thus helping to fight infections.  Antibodies recognize a unique part of a foreign target called an antigen and then launch an attack against the pathogen.  The cascade of attack which follows is called inflammation.

ANA – Antinuclear Antibodies

This test detects antinuclear antibodies in the blood.  In contrast to the description above, the antinuclear antibodies often attack the body’s own tissues.  They identify normally occurring proteins in our bodies as foreign, dangerous.  Although this is not always the case, a positive ANA test indicates that the immune system is attacking  one’s own tissue — an autoimmune reaction.  Some autoimmune disorders are SLE, Scleroderma, Sjogren’s Syndrome, Polymyositis, Mixed Connective Tissue Disease, Drug-Induced Lupus, and Autoimmune Hepatitis.  Having said this, a positive ANA test can be found even when someone’s healthy.

Fast facts about ANA

·       A positive test signifies the presence of the ANA in the blood.  False positives are possible.

·       95% of those with SLE will test positive.

·       By itself it neither indicates the presence of disease nor the need for treatment.

·       3%-15% of all healthy individuals will test positive for ANA.  This increases to 10%-37% in those over age 65.  Some medications can cause a positive ANA.

·       Those who test negative for ANA do not have SLE.

·       Autoimmune disorders can be treated, not cured.

·       A Rheumatologist interprets the ANA in the light of the signs, symptoms, and other results.

The other antibody blood tests.

These are often taken together with the ANA to check for the presence of other specific antibodies.  Theseinclude:

  • Anti-SS-A (also called Ro).
  • Anti-SS-B (also called La).
  • Anti-dsDNA.
  • Anti-RNP.
  • Anti-Smith (Sm).

These tests often positive in SLE, but not all of them, not always.  They can help in acquiring a diagnosis together with the clinical criteria.

·       Anti-SS-A and Anti-SS-B: not specific for SLE but useful in women with SLE who are planning a pregnancy.  Positive such tests might predispose to Neonatal Lupus or congenital heart block.

·       Anti-dsDNA – Anti double stranded DNA antibodies fight against DNA.  Usually seen in SLE.  Can be repeated at intervals to check disease progression.

·       Anti-Sm – specific to SLE and may be associated with more severe cases.

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